Here is my advice:
Do some research on your PC. Look in your manual for your sound card, or look it up on the web. See which jack is for a mic input and line in input. Like others have said, it's most likely going to be an 1/8th inch stereo jack.
You can plug a mic into the mic input, but you'll need to make a trip to the store for a couple things. If your mic has an XLR jack, you'll need to purchase a cable that is XLR at one end and 1/4 in jack on the other. I've yet to find a calbe that is XLR-1/8in. Then you'll need to buy an adapter that converts the 1/4in jack to 1/8th inch. You can then plug that into your mic input and record.
The 2nd option is to buy yourself a cheap mixer (Behringer works fine for me). You can use eithe the 1/4in or RCA outs on the mix to go to the line in jack on your PC. You'll need to go and purchase a cable that's either Stereo RCA to 1/8th inch or a Y cable that has to 1/4 inch jacks on one end and an 1/8th inch stero jack on the other. You'll plug the 1/8th inch jack in the line in on your sound card.
Lastly you can look into upgrading your sound card to something that's set up for recording. I've been using a Midiman Audiophile 2496 for over a year, and it's a great card for aboug $130 at newegg.com . This card has RCA jacks for analog input, but it also has S/pdif for a digital signal.
I hope this helps! I'm new to this board, but I've been working with my gear for a year or two now. My best advise is to use google often. The more you learn about your craft, the better you'll be at it.