A web browser is a piece of software, which is installed on your computer. This software, otherwise known as an application, allows you to load and view the contents of an internet page.

Without this software installed, you would not be able to view any web pages on the internet.

In a word, compatibility.

Over the past few years Microsoft with their Internet Explorer and Netscape with their Netscape browser, have battled it out to be the dominate browser on the market. This has resulted in most of the new developments in internet programming, originating from either of these two companies, as they have attempted to "out innovate" each other.

Thus most of the new standards, programming code and rules that now run the internet, are reflected in the way that Internet Explorer and Netscape work.

So, for the sake of compatibility and standardisation, it is best to stick with one of the above mentioned browsers.