Selenium consists of three major components. These parts are:
WebDriver allows direct communication of web browser by using its native compatibility for automation. RC component provides APIs for different programming languages like .NET, PHP, Java, NodeJS etc. It is compatible with most of the browsers.
Selenium IDE is an integrated development environment tool to record and playback. It is a firefox plugin. Practically, I have used Selenium IDE on Firefox 50.0 version. However, support for the current version may vary.
You may download Selenium IDE FireFox extension here.
To distribute tests on multiple machines for running tests parallel to save time, grid can be used.
