Wow. The number one newbie question.
What kind of microphone is it? If it's a cheapo walmart mic you won't get very good results. They won't even be adequate.
Regardless, you really can't just plug a microphone into your soundcard unless it's a "computer microphone".
Without going into details, here's what you need at a bare minimum:
1) A microphone.
A Shure SM57 or SM58 would be the cheap standard. $70 to $100
2) A preamp. You NEED a preamp of some sort to get the mic signal to a line level that can run into your computer.
3) A decent soundcard. Many soundcards perform VERY poorly for recording. You will be running the preamp into the LINE IN port on your soundcard. If it sounds like absolute hell, spend a measly $30 on a Soundblaster PCI128 or Ensoniq AudioPCI. They're not great, but they work well enough.
If you do a little searching on this subject you will find a LOT of information (in this forum alone). I'll bet that every one of us at one point tried plugging a microphone into a soundcard and ran into the same wall you've smashed into.
Slackmaster 2000