I guess you want to insert force or constraint in a certain area of a face? In that case, the answer is as following:
First create a sketch on a face you want to split. Then go to Surfacing → Split (in Modify Surfaces module)
then click on the face you have created the sketch on to and right-click. Then choose the outer lines of your skecth and right click again.
Now you should have a splitted face where you can insert forces and constraints. This was done in SE Simulation, not in Femap.
To split the body you will have to create a surface or reference plane at the boundary and then use the Boolean command "Split" to split it into multiple bodies (Note: This is now a Multi-Body part and you will see new nodes in pathfinder).