They both are fully jointed and have portal guns.
The steps for each part are in the photos, the pieces you need to add are highlighted.
Step 1: Begin Atlas.
Start with Atlas' main body.
The first pictures are the pieces you need to build him.
Step 2: Arms.
Step 3: Legs.
Step 5: Begin P-Body.
First his torso.
The first picture is the pieces you need to build him.