Dear Kristi,
Hi. Since you are "Type O" you are compatible to donate a kidney to a donor of any blood type (and the "+" or "-" does not matter in kidney transplants). However you also have to pass a "crossmatch" to see if the intended recipient has particular anti-bodies that would react against an organ from you.
If it turns out that you are NOT compatible to donate to your friend, you could also offer to take part in a "swap" in which you would donate to some one else, and that person's willing but incompatible donor would donate to your friend.
If you go to the homepage of this site you can click the line about living donation to read more in detail about the testing process. Take you time and get well informed about living donation, including its risks.
The "forum" at this site is the best place to post further questions.
best wishes,
Fr. Pat