How do I play Jungle Vayne?

You don't

You clear the camps then go to a lane and kill the enemy champions. After that take towers until you can take the nexus

im assuming its kind of like yi where you AFK farm because you are so strong late game. But I haven't played it.

You are going to have a miserable time if you even try jungle Vayne, and silver bolts damage is capped against monsters. She has pretty mediocre clear times and no AOE at all (Don't try a Runaan's to offeset that)

So you probably start , get a leesh from your bot on your first buff. Upgrade refillable into and you'll probably just build and play like master Yi.