While you automate a test case using Selenium, all actions that you want to perform on the web application can be done by finding the appropriate XPath variable of the elements that are visible on the screen. For example, if you need to click a button named Create, you need to find the XPath variable of this button. An XPath variable uniquely identifies an element present on an XML document.
A FireFox add on, XPather, allows you to identify the XPath variable of the element. You can right-click the element and click Show in XPather. Click here to install XPather.