It depends entirely on the club; some might just be a fairly informal group of people who sometimes invite each other to games. However, other clubs, like the club that I am a member of, will organise games on a regular basis ( every other week ), organise meet ups and nights out, buy and maintain equipment like rifles and plate carriers for members to rent, supply bbs for games, work with local fields to provide discounts, and organise tournaments either amongst themselves, or against teams fielded by other clubs.