Snapping multiple vertices but picking which one is primary I'm having trouble figuring out how to snap multiple vertices but selecting by which one the position of all of them is adjusted. 

Right now I can't be precise because I'm not able to align edge to edge because of this. I'm coming from 3DS Max and that was something I was able to do by just picking which vertex is main one.
For the vertex you want to snap, in the Snap options, you have the choice between Target > Closest / Center / Median / Active. To point out the vertex you want to snap to, use your cursor.



For example Active will snap the last vertex you've selected.