Creating a world for an online game?

I have only created people, animals, and objects. I want to create a world, example. hills, grass, dessert, ocean, bridge over a cliff,some mountains, lakes, caves, rocks, trees and so on. Where is a good tutorial to create this kind of work for an online game so it wouldn’t lag the game with too many poly’s. Someone not so detailed something simple. I tried looking for tutorials and can only find ones that are create with ease with too much detail that wouldn’t work for an MMORPG game. Can anyone help?I would much appreciate it.

You should try to post in the Game Engine part of the forum, you’ll certainly have more replies. Because it’s not just low-poly modeling as it involves textures tricks, like alpha maps for plants or leaves.