Why Automated Testing ?
We all might have least used one of these following web technologies in the past, like HTML, PHP, JavaScript ..etc. But have you ever though of writing a code to test website written in any one of the above technologies.
If you do though about testing website, I can tell that you wouldn't have thought of Automating those testing.
As it is important to code our webpages and website user-friendly, it is also needed to test them in real time for ensuring whether they are working as expected.
For a simple and clean webpage written in HTML without too much transition between pages won't really need an automation in testing them but considering an Website with several page transition and functionality then an automated testing solution is needed in order to test them to reduce the time and human interaction needed.
These automated testing are also prone to mistaken and can be used to perform testing of website on several iterations.
Why Selenium?
The real reason is that there are no better option out there other than selenium. Seriously? I hear you, yes really there is not other option comparing all the below factors,
1. Cost - You actually don't have to pay for using it.
2. Compatibility - Supports several browsers including IE and supports several Platforms.
3. Support - Several developers and professional uses Selenium for the Web testing and there are lots of active forum available to answer you queries.
4. Easy to Use - Several methods in selenium are petty much self explanatory and easy to run and debug.