Yup, this question is waaay too general...try doing some research before asking people to write a novel for you. Right now a response to your question boils down to two things: what type of gear do you have? What are you willing to spend to upgrade that gear? If the answers are "nothing" and "nothing," then you could get a 1/4" to 1/8" converter at radioshack for about $2, and get a decent sound by running your guitar directly into the LineIn jack on your PC. But it won't sound 1/1000th as good as a cheapo, well positioned $70 mic through a cheapo $70 preamp (for which you might still need that $2 converter).