Let's start from Selenium IDE
Selenium IDE is a record and play back tool. We can download it from http://seleniumhq.org/download/. Its a firefox plugin and we can automate and run only in firefox.
Click the download link of latest Selenium IDE, Browser will show an information bar, click Allow then a pop up window will prompt, Click Install Now. After installation it will show another information bar as Restart firefox to complete your changes. Click Restart firefox.
Thats all !
You can find Selenium IDE from Tools Menu.
Click the following link to view how to record and play back.