NEWBIE desperate for help MUSIC RECORDING

I have a pretty good computer and the sound card is kind of messed up. I
want to record music on this computer and am thinking about either buying
a new sound card, or buying a mixer to plug into the sound card. What's
the difference?

Anyone know of a good soundcard that I can plug a guitar into? And has
XLR inputs?

What's the difference between a soundcard with mutliple inputs, and a
soundcard hooked up to a mixer?

Thanks everyone. I really appreciate it.