Need A little helpen'

I have a problem, when I want to add terrain like hills and mountains, my first person character fall right through the floor, and when I use the cube to try and edit it to look like hills, it does not comply.

Hi, welcome to the forum!

Does your terrain object have a collider? If you are using Unity’s built-in terrain then check the object has a terrain collider. If you are importing the terrain mesh from a 3D app then you will probably want to use a mesh collider.

Long shot but, are you using Windows 7 by any chance?

Using Macintosh OSX Snow Leopard.