First, your have to download and install Firefox. Go to www.getfirefox.com, click the "Download Now" button, click run. Then let it download, then follow the prompts to install Firefox. After that, simply go to your desktop, or into your Start button, and you have Firefox there. You can have it import data from your old browser (IE, Safari, Chrome, etc.) or simply start fresh. Use it like a normal web browser!

You can read Installing Firefox for some more tips and screenshots to help you out.

Oh I just say you posted this twice, sorry about that.

https://support.mozilla.org/en-US/questions/924458

Now, if you are having trouble beyond installing Firefox, you can use the search page to search for things using Google, or up in the address bar (where it probably says about:home or "go to a website") you can go to specific websites such as www.facebook.com, etc. You basically use it just like you use any other web browser (like Internet Explorer).

You can also read https://support.mozilla.org/en-US/kb/how-do-i-install-firefox-and-get-started