you need to create a level. (either in wed, or by script)

by script:
make a terrain in med and load it as level using level_load("myterrain.hmp");

then you have a level.

again assuming that you dont use wed. You need to load models by script(create entities)
ent_create("mymodel.mdl",position vector,function);

then you have model loaded.

this goes on like that, for step by step tutorials, see lite-c workshops in donload page.