The Selenium API defines dozens of commands that can be categorized into the following:

• Actions
• Accessors
• Assertions

Actions: Actions are commands, to change the state of the application like clicking links or buttons, select an option in a <select> or type a character sequence in a given textbox.

Commonly used Selenium Action commands are:

• Open: This will open the specified address
• openWindow (url,windowID): Opens a popup window.
• select: This will select the specified item in a list.
• select (selectLocator,optionLocator): Select an option from a drop-down using an option locator.
• selectWindow (windowID): Selects a popup window using a window locator; once a popup window has been selected, all focus shifts to that window.
• store (expression,variableName): The name of a variable in which the result is to be stored and expression is the value to store.
• type: Sends text input to an element.
• type (locator,value): Sets the value of an input field, similar to user typing action.
• typeKeys (locator,value): Simulates keystroke events on the specified element, as though you typed the value key-by-key.
• Click: Clicks the element at the provided location
• Click (locator): Clicks on a link, button, checkbox or radio button.
• clickAt (locator,coordString): Clicks on an element with the help of locator and co-ordinates
• Check: To toggle the value of checkbox.
• contextMenuAt (locator,coordString): Simulates opening the context menu of the specified element from a specified location
• dragAndDrop (locator,movementsString): Drags an element and then drops it based on specified target.
• echo (message): Prints the specified message on console which is used for debugging.
• fireEvent (locator,eventName): Explicitly simulate an event, to trigger the corresponding "onevent" handler.
• focus (locator): Move the focus to the specified element.
• highlight (locator): Changes the background Color of the specified element to yellow Briefly which is useful for debugging purposes.
• mouseDown (locator): Simulates a user pressing the left mouse button on the specified element.
• mouseDownAt (locator,coordString): Simulates a user pressing the left mouse button at the specified location on the specified element.
• mouseUp (locator): Simulates the event that occurs when the user releases the mouse button.
• mouseUpAt (locator,coordString): Simulates the event that occurs when the user releases the mouse button at the specified location.
• pause (waitTime): Waits for the specified amount of time (in milliseconds).
• refresh(): Simulates the user clicking the "Refresh" button on their browser.
• waitForCondition (script,timeout): Executes the specified JavaScript snippet repeatedly until it evaluates to "true".
• waitForPageToLoad (timeout): Waits for a new page to load.
• waitForPopUp (windowID,timeout): Waits for a popup window to appear and load.
• windowFocus(): Gives focus to the currently selected window.
• windowMaximize(): Resize currently selected window to take up the entire screen.

Accessors:

Accessors search the state of the application and store values in variables. Eg: "storeText". They are also used to generate Assertions automatically. 

• Store: This will allow storing a value temporarily.
• Verify: Performs a soft assertion against an expected value.
• Assert: Performs a hard assertion against an expected value.
• waitFor: Waits until the value matches the specified value.

The following are more commonly used Selenium Accessors commands:

• assertErrorOnNext(message): Pings Selenium to expect an error on the next command execution with an expected message.
• storeAllButtons(variableName): Returns the IDs of all buttons on the page.
• storeAllFields(variableName): Returns the IDs of all input fields on the page.
• storeAllLinks (variableName): Returns the IDs of all links on the page.
• storeAllWindowIds (variableName): Returns the IDs of all windows that the browser knows about in an array.
• storeAllWindowTitles (variableName): Returns the names of all windows that the browser knows about in an array.
• storeAllWindowNames (variableName): Returns the titles of all windows that the browser knows about in an array.
• storeAttribute(attributeLocator, variableName): Gets the value of an element attribute. The value of the attribute may differ across browsers.
• storeBodyText(variableName): Gets the entire text of the page.
• storeConfirmation(variableName): Retrieves the message of a JavaScript confirmation dialog generated during the previous action.
• storeElementIndex(locator,variableName): Get the relative index of an element to its parent (starting from 0).
• storeLocation(variableName): Gets the absolute URL of the current page.
• storeSelectedIds(selectLocator,variableName): Gets all element IDs for selected options in the specified select or multi-select element.
• storeSelectedIndex(selectLocator,variableName): Returns index (option number, starting at 0) for selected option in the specified select element.
• storeSelectedLabel(selectLocator,variableName): Returns label (visible text) for selected option in the specified select element.
• storeSelectedValue(selectLocator,variableName): Gets value (value attribute) for selected option in the specified select element.
• storeSelectOptions (selectLocator,variableName): Gets all labels in the specified select drop-down.
• storeTable(tableCellAddress,variableName): Gets the text from a cell of a table.
• storeText(locator,variableName): Gets the text of an element.
• storeTitle(variableName): Gets the title of the current page.
• storeValue(locator,variableName): Gets the (whitespace-trimmed) value of an input field.
• storeChecked(locator,variableName): Returns whether a toggle-button  (checkbox/radio) is checked.
• storeElementPresent(locator,variableName): Verifies that the specified element is somewhere on the page.
• storeTextPresent(pattern,variableName): Verifies that the specified text pattern appears somewhere on the rendered page shown to the user.
• storeVisible(locator,variableName): Determines if the specified element is visible.
•  

Assertions:

Assertions are like Accessors, but they verify that the state of the application is as expected. Selenium Assertions can be used in 3 modes:

• Assert
• Verify and
• waitFor. 

The following are more commonly used Selenium Assertions commands:

• waitForErrorOnNext(message): Waits for error. Used with the accessor assertErrorOnNext.
• verifySelected(selectLocator,optionLocator): Verifies that the selected option of a drop-down satisfies the option Specified.
• waitForSelected(selectLocator,optionLocator): Waits for getting the option selected; used with the accessor assertSelected.
• waitForNotSelected(selectLocator,optionLocator): Waits for not getting the option selected; used with accessor the assertSelected.
• verifyAlert (pattern): Verifies the alert text.
• waitForAlert (pattern): Waits for the alert; used with the accessor storeAlert.
• verifyAllButtons(pattern): Verifies the button.
• waitForAllButtons(pattern): Waits for the button to load; used with the accessor storeAllButtons.
• verifyAllLinks (pattern): Verifies all links; used with the accessor storeAllLinks.
• waitForAllLinks (pattern): Waits for all links; used with the accessor storeAllLinks.
• verifyAllWindowIds(pattern): Verifies the window id; used with the accessor storeAllWindowIds.
• waitForAllWindowIds(pattern): Waits the window id; used with the accessor storeAllWindowIds.
• verifyAttribute(attributeLocator,pattern): Verifies an attribute of an element; used with the accessor storeAttribute.
• waitForAttribute(attributeLocator,pattern): Waits for an attribute of an element; used with accessor storeAttribute.
• verifyBodyText(pattern): Verifies the body text;
• waitForBodyText(pattern): Waits for the body text; used with the accessor storeBodyText.
• waitForConfirmation(pattern): Waits for confirmation; used with the accessor storeConfirmationPresent. 

Locators

Selenium uses locators to find and match the elements of web page that it needs to interact with.

There are 8 locators in Selenium are:

• Identifier: works with the id and name attributes of your html tags.
• Id: Select the element with the specified "id" attribute.
• Name: Select the first element with the specified "name" attribute.
• Link: This is intended to select links only and selects the anchor element containing the specified text: link=the text of the link.
• DOM: This is works by locating elements that matches the javascript expression refering to an element in the DOM of the page.
• XPath: To locate an element using an XPath expression. XPath is the standard navigation tool for XML; and an HTML document is also an XML document (xHTML).
• CSS: The CSS locator uses CSS selectors to find the elements in the page.