Making money
The first way making money with 3d is you sell the endproduct of your work.
The picture or the animation you have produced.
Animations are made on demandand achieve a fair price , while with luck, on a picture you get asked to sell it,
Fiew are that lucky though, grin.

Next thing you can be asked to do is custom modeling.
Someone does a game or an artproject and needs some 3d models he asks you to do.
Usually if you dont work mainstream, its not worth the effort, because you get paid in shares of the profit, and most small projects are bound to fail.(call it expirience ) lol.
I almost never indulge on projects like those.

A good market though is to provide content.
Many 3d artists do not have the capability or time, to model or texture themselfs.
They buy models and other 3d content, on internet sites that have specialised on brokering 3d content.
I eg sell plain 3ds (format) models and texturetiles, but have allready expandes my skills to produce ready to use Poser content.

Some of the productlines i broker you can see below
Age of darkness Vol. 1
The Federal Forces
Modular materials Vol1 : Metals