One of the hardest thing for beginners is tuning your guitar. There is a lot of advice out there about the best method, I leave that up to you to decide, according to your needs and resources. Some good places to start looking can be found on the GuitarSite.com Tuning page:
http://www.guitarsite.com/tuning.htm

Before you can play anything you need to have a tuned Guitar. The standard tuning for a guitar is:

STRING / NOTE
6th string(the fat one) E
5th string A
4th string D
3rd string G
2nd string B
1st string(the thin one) e

I suggest buying a tuner that does all the work for you. A good tuner can go for 10-50 bucks at any guitar retailer. But if you're too lazy or too poor to get one, there are alternatives...

MORE...

Start here, of course: http://www.guitarsite.com/tuning.htm

see also:

Tuning down a 1/2 step, and how do I do it
http://www.guitarsite.com/database/Guitars/rec/114/

Dropped-D Tuning
http://www.onthenet.com.au/~kirkclan/dropd.htm
Kirk Lorange writes: "I discovered Dropped-D tuning years ago. D was a good key for my singing (if you can call it that), and I loved the way that D chord sounded with that low note ringing..."

Finally, a High E Tip...

Replace your "g" string with a high "e" and then tune it up to "g". This is a variation of Nashville tuning which uses all octave strings for the wound strings, i.e. a twelve string tuning without the bass strings. This set-up produces a novel rhythm guitar sound with or without a second normal rhythm guitar.