sorry if i'm being mean but did you happen to select both vertices by mistake? or are the vertices like 10 units away and there's absolutely no chance at all that you could select both of them without selecting others?


as for snapping, the the snapping options are at the top of the screen as little square buttons

but since using the mouse to go up there always takes forever and triples the time it takes to do anything, use the hot keys

x, c, and v
x to snap to grid, c to snap to points, and i dunno what the other thing does because it never snaps to anything

also useful is being able to snap a vertex to another one but only in one axis. in that case you just move the vertex using the arrows on the move tool that you see in your scene

(did that last paragraph confuzzle you? i dont think i said it very well...)