Paintball forums are a place to vitually hang out with friends, acquaintences and complete strangers and get advice, tips or just to tlak paintball. Forums are also a great resource for learning about paintball by reading through old posts as well as a great place to buy and sell gear.
PBNation is the largest paintball forum with a very active community and lots of dedicated moderators and posters. If you want to alk paintball, PBNation is the place to start. PBNaiton does tend to attract more than its fair share of young, immature posters which can make reading a thread a little teadious at times.
MCarterBrown is a good-sized forum with a lot of information with a lot of very knowledgeable posters. It isn't as large as PBNation, but it is still a great place to visit.
Automags.org is not as commonly frequented as other forums, but it has a huge wealth of information in its archives as well as many dedicated posters who are very knowledgeable about the sport. This forum has regular posters who have been with the sport for many years and give it a slightly more mature feel.
Special Ops originated the phrase "We Are Woodsball" and the forum has followed that mantra to a T. This forum is a great resource for those who are interested in woodsball, milsim and outlaw paintball.
I add this forum only as a resource to search through as it does have a large collection of older, useful content. Currently it is basically dead with little new activity, but valuable information is available with a simple search.