Are you going to keep it in a container? If so, what do you plan to train or trellis it to? i.e., you can set the pot next to a fence or trellis and leave it there, or you can put a small trellis structure IN the pot and train to that so that the pot can be relocated any time, or you can just keep it in the pot and keep it trimmed as needed.

Grapes grow quickly when they're in the ground... not sure how they'll do growing in a pot.

I have to keep it in the pot, small yard. So I will put a trellis (not sure what shape) in the container. Wondering if I need to prune at this point, or just start training it on a trellis.

In that case, I would choose a shape/structure and begin by using a twist-tie to loosely hold the branches in the desired position... then I would prune away or cut back any branch that fights that shape or goes in the wrong direction. Good luck!

Sounds simple enough - thanks!