If you already have Firefox installed you can ignore this.
Firefox is a free web browser that works much better than Internet Explorer. Internet Explorer is also free of charge but closed source proprietary software owned by Microsoft corp. Firefox is a Open Source meaning that it's development is a community effort.
Perhaps you don't care one bit about the politics of software creation, but you might actually care about how you browse the web. I personally abandoned Internet Explorer years ago after many many years of using it. Firefox just works better, is faster and the usual software politics.
So, if you're stuck with that lame Internet Explorer, get your arse in gear and install Firefox. It's just a click away Trust me. It's worth it.