Hi Jimmy, some CAD software is set up to have different modules for creating one "part" like you're talking about and then a different module for making an "assembly" made out of the parts. But MoI (and Rhino too) are not set up like that, in MoI you just work in one environment and you can create as many different objects in that environment as you want. To put parts together you would use tools like the Transform > Move command using snaps to locate points precisely on to your objects.

But if you're talking about something like a simulation where you want to test how parts will move with each other, a more traditional solid modeling program something like SolidWorks or SolidEdge may be a better fit for that level of mechanical design, they have tools for doing that type of thing, while MoI is focused just on modeling and not on simulation.

- Michael