Beginner question

[ach217217]

All,
I am an inexperienced user trying to learn abaqus/CAE.  I need to create a simple analytical rigid surface with a deformable membrane attached on top.  I have created a part for each.  How do I attach the two parts?  Also, how do I apply boundary conditions with the rigid surface (error says BC cannot be applied in this case)?  Any help is greatly appreciated

Thanks