Technology...we all love it when it works, but want to throw it out the window when it doesn't. It can make our lives better and it can complicate our lives beyond belief.
I would wager that all of us use the Internet every day, multiple times a day, and some of us every minute of every day. To that end, we all use Internet browsers to "surf" the web: Internet Explorer, Safari, Firefox, and Chrome seem to be the 4 most of us use on a regular basis.
Website standards are always changing. Hackers are always trying to find another way into your computer through your browser. The technology powers that be are always updating their browsers to stay ahead of (or react to) those hackers and to make sure the websites you visit look and feel the way the designers intended.
Keeping your browser up to date is an easy defense against drive-by attacks (meaning your computer could possibly be compromised just by visiting a malicious website). Most browsers have a built-in update function to either manually update or automatically update once updates become available. This function either happens when your computer checks for updates (Apple Safari and Microsoft Internet Explorer) or there is a drop down menu button that allows you access to this function (Google Chrome and Mozilla Firefox).
Everyone has a favorite browser. At times, I've found a website that only works with (or works better) with another browser; therefore, I keep 2 browsers on my computer to have a backup in case I need it.
It's safe to say that the computer you are using right now either came with Apple Safari or Microsoft Interenet Explorer as a default. I would suggest you either keep Firefox or Chrome as a secondary browser, should you run accross a website that requires a different browser than the one you are using.
As a side and final note, be sure to keep your installed plugins up to date as well (flash player, adobe reader, etc) as that is another avenue that malicious websites can use to access your computer or even plant something nasty).