There are many ways to earn money on this bitcointalk forum. The first is popular one, signature campaign. The second is on games and round section, on this section, you can check many thread that give you free bitcoin.
Another section is the services section. There you can offer your talents such as avatar & signature designing, photoshopping, translating etc. You could also sell your goods on bitcointalk in the goods section. You can sell almost anything there- I once saw someone selling used panties....