how can i make cutom objects to put into may maps?

hi guys!
im quite new to making maps for Beamng, and i was wondering if someone could provide me with a guide on how to take objects that ive created in blender or sketchup and prepare it so that i can put it in the game using the level editor as an object? also i want to know how to set the materials correctly..
any help is greatly appreciated

 

thanks for pointing out!