Need help!

Hello!

im all new to this types of programs, i have nevert done anything like this before..

but my problem is that everytime i add for example a terrain, it dosent sit in its place, when i try to zoom the terrain just dissapears under the platform that u are supposed to place the terrain?

if anyone understands what im tryin to say here, please respond! thanks!

the terrain follows with my zoom, so when i zoom in its goes below the ground, and up when i zoom out..