What is surprising is the lack of grounds. Those devices don't appear to be the self groounding type (and unless you're fed with conduit or type AC cable, the box isn't either).

The rest looks pretty straightforward. The red is the unswitched feed, the black is the switched hot, the white is the grounded conductor. If you connect the black wire that is connected to the receptacle to the red wire on the switch, it will be hot all the time, not switched. Other receptacles you don't show, but they will also need to be connected the red wire.

It appears that the cable coming into that junction box is a switch loop. Having also a neutral also allows that receptacle to function.

You'll need to find the other end of that cable, and what else comes into that junction box, to see if separating the receptacles will be easy or difficult.