Level Design is the process of creating 3D environments or "worlds" for players interact with video games on their PCs or on game consoles machine.
Basically, designers use level editing software to build 3d architecture, then apply textures or shaders, also known as materials to the surfaces of that architecture so that players can see it in the game.
Portfolio
The portfolio below is comprised of screenshots of various levels that were designed for Jedi Knight: Jedi Academy, a popular FPS game, that was built using Q3 engine technology.