How to make small model and item for display it

So I want to try making mod that having figure in it (similar to mod name "MiniHeads")

but I am not even sure what to do for making it.

And other thing is I want to make item like Display Case same as in MiniHeads mod (basically a item I can place multi figure in it) but I am not sure does it require anything special to make it work or not (since normally you can't place item inside item and make it display right)