I’m coming from 3ds max trying to learn Houdini. When I’m modelling in 3ds max I can just click and object hit shift and drag and than I can create an instance or copy, you can even select faces on the model and than shift drag them and create a copy of just the faces not the whole model.
I can’t figure out how to do this in Houdini?

Not quite as slick, but there is the duplicate tool to copy an object or geometry selection.

Tab menu -> Duplicate

For individual elements (primitive selection) Use the extract tool, which creates an object merge node. You may need to switch the ‘merge into object’ to None to allow transforms to affect the new object.

Tab menu -> Extract

Instancing is rarely done using non-procedural methods such as these, but if desired, you can create an instance object, and then pick the source object to be instanced. There is no tool to allow automatic instancing of a selection. Usually instancing is done using template points that are created procedurally. Non-procedural workflows for instances are currently lacking/clunky.

I just want to add to what jsmack said… I too come from 3ds Max and what I've found is that a lot of the time when I would have made an instance of an object in max, in Houdini what I end up doing is just build an HDA… Which is really the analog to xref in max but Houdini does them a million times better. In general I've found that allowing myself to be be fast and loose with HDAs to be a really powerful way to work.

As mentioned, duplicate sop, or use a transform sop and merge with the original.
To do it at /obj level use an object-merge sop in a new geo object that references what you want to instance, set it to ‘merge into this object’.

There's a few other ways to do this, but more suited for mass duplication/variation.