Marine F-35B: STOVL so it can take off and land on the smaller Marine helicopter carriers (but not carry as much fuel or ordnance) (look up Wasp-class amphibious assault ship)
Navy F-35C: no STOVL, heavier landing gear, tail hook, and bigger wings so it can land on giant Navy supercarriers (while carrying almost as much stuff as the Air Force variant)
There are three variants:
This was an F-35C.