ABAQUS CAE assembly analysis

I am currently working on a robotics project where we now want to do FEA analysis on the structure when it runs into something, or falls of a ledge. I have some experience with abaqus, but most of it involves analysis (static, dynamic, thermal, frequency, etc) on a single part or between two. up until this point i have been able to find lots of help on the internet via tutorials and examples, but i cannot figure out how to properly constrain and define the joints of a fully functional mechanism, and there does not seem to be any online help. I have all the parts saved in STEP files, and have imported and meshed all of them, but i cannot seem to properly define the interaction/contact between parts, in particular when defining how parts are screwed together. i am not asking to be hand-held through this, just looking for some advice, or if anyone knows any tutorials/examples of this that are not in the User's Manual, which i have read through.

thanks