Terrain Level Detection

Hello, maybe this is a ‘poor’ question but I really need some help.

I’m going to make my first 3D game using OpenGL. I use 3D Studio MAX to create my terrain and convert it to *.cpp using 3D Exploration. The question is, how can I make my ‘hero’ walk on various terrain level like hills,stairs,etc. By now,I only know how to move ‘him’ on a flat terrain.

For your information, I’m using glut3.7