[RoboDesigners]

Just like in real life, constraints are used to link parts or assemblies together in an assembly. So, constraints are only available when you are working in an assembly file (*.iam)

As far as I know, constraints just "anchor" a piece in one axis. (I'm new to CAD too, so I there may be more to constraints than just that...) So, if you want to just anchor a module on a piece of plastic, you must constrain it 3 times:

Constraint 1. Bottom of module to plastic piece (offset = 0in)
Constraint 2. Front of module flush to front edge of plastic sheet (offset = However many inches you want, I used 5in)
Constraint 3. Side of module flush to side edge of plastic sheet (offset = However many inches you want I used 5in)

Here are some pictures to illustrate.

If you can't get the constraint tool to select what you want it to, (i.e. it's selecting an axis instead of a plane), hover the mouse and click the arrows that appear below the current constraint. (Constraint3selecting.jpg)

Hope this helps!
Andrew