Below is the list of selenium components -

• Selenium IDE
• Selenium client API
• Selenium WEBDRIVER
• Selenium Remote Control
• Selenium Grid

Selenium IDE 

Selenium IDE was created with the intention to increase the speed of test case creation. It records user action and playback which helps you create simple tests quickly. The interface is user-friendly and also supports multiple extensions.

Selenium IDE(Integrated Development Environment) is an open-source software testing TOOL for web applications and Firefox Add-on and chrome extension. Without paying a single penny Testers and web developers can use and download it. The purpose behind Selenium IDE is to increase the speed of test case creation and it allows to edit, record and debug the tests. It helps the users to record tests quickly and playback tests in the ACTUAL environment that it will run in.

Selenium client API

Selenium IDE has its very own scripting language called Selenese, which provides options for clicking a link, selecting something, retrieving data from opened pages. Instead of writing tests in Selenese, these tests can also be written in different programming languages. Tests communicate with selenium by calling methods in Selenium Client API. Selenium provides client APIs for Java, C#, Ruby, JavaScript, R, and Python. With Selenium 2, a new Client API is introduced with WebDriver as its central component.

Selenium WebDriver

Selenium WebDriver is a collection of APIs used to automate web application testing. It is a framework to automate a browser that accepts commands and sends it to the browser through browser-specific drivers. WebDriver control browser by communicating with it. Selenium WebDriver supports Firefox, Chrome, IE and Safari browsers and Java, C#, PHP, Python, Perl, Ruby programming languages. It is designed to provide a simple, CONCISE programming interface. It enables a user to use a programming language of their choice to write test scripts and enables them to use conditional operations, looping and other programming concepts which helps to make test script robust.

Selenium Remote Control

Selenium RC(Remote Control) is a tool that allows creating automated web application UI tests in any programming language.

Selenium RC is composed of two components

1. Selenium Server

It LAUNCHES and kills browsers and interprets and runs the Selenese commands passed from the test program. For browser request, Selenium server acts as an HTTP proxy by intercepting and verifying HTTP messages passed between the browser and the AUT. In short Selenium Server receives Selenium commands from your program, Server interprets commands and reports back results of running test to your program.

2. Selenium Client

Client libraries provide the interface between a programming language and the RC Server. Client libraries of different programming languages, instructs Selenium Server how to test the AUT bypassing server test script's Selenium commands.

The client libraries allow you to run Selenium commands from a program. Each supported language has a different client library. The selenium client library provides a programming interface (API) that runs Selenium commands from your program. Each interface contains a programming function that supports each Selenese command.

The client library gets Selenese command and passes it to the Selenium Server for processing a specific action on the application under test (AUT) and receives the result of that command and sends it to your program. Your program stores received result into program variable and report is a success or failure.

Selenium RC is used to execute scripts on different browsers as RC supports multiple browsers like IE, Firefox, Chrome, Safari, Opera, etc.