I want to build a virtual environment, to build the stuff that habit the virtual world i can read values from a database? For example, have stored the buildings data in a mysql database (textures, dimensions, positions)? Or wich is the most effective way to do it?
Can i make that world interactive like Second Life or OpenSim? Can i make him to support multyplayer and the players communicate between them?
I've been searching and it seems all possible but i'm starting and i would be thankefull if there is any confirmation of that and (if possible) tips on how to do it because i just dont know where to start from to create this virtual world(first the terrain? the controls? load the textures?)
short answer, yes. The company I last worked for did something along these lines. It's a very very big task if you want to do this all by yourself though.
I would recommend creating the terrain first if you are asking in what order to do things in, so that you can get a visualization of what your world will be based on: the natural terrain. After that, you should work on creating your buildings to get an idea of what the players will be walking around with. Then you should start working on the scripts and controllers and whatnot, but definately first you should create the actual visual world to get an idea of how you want the characters to interact.
You'll need to decide on a database (Postgres, MySql, etc). Some handle 3D natively, others you'll have to roll your own. Secondly you'll need to load models on-the-fly. There are some OBJ loaders, and an X3D loader is in the works. Then you'll need to figure out how to 'wire up' interaction to make the world more interesting than just a place to walk around in. It's a huge project, believe me. But if you'd like to contribute to such, message me.