Firefox is a web browser, the same type of software as Internet Explorer. It is used to browse websites and visit all the pages you like, in much the same way as Internet Explorer.
The difference is that Firefox is open source. Firefox is the peoples web browser. Firefox is more secure. Firefox is more customizable. Firefox provides more consistent page rendering. Firefox promotes competition in a market dominated by a monopoly. Firefox provides a consistent platform across operating systems. Firefox is free. Firefox is fast. Firefox provides more protection. Firefox is a trendsetter. Firefox has style.
Do your research and find out for yourself.