How can I get Blender to snap vert using grab command? So I am taking a short course modeling house on Udemi. I noticed that when I use extrude command it is very easy to snap to another vert. However, at one point we need to subdivide (basically one vert missing) to help with making a wall. The teacher just grabs this vert, constrains it to x and snaps it in-line with another vert. 
My blender will not do that, even if I have the same snapping settings on as the teacher's Blender.
Blender seems not to notice the vert I want to snap to while grabbing, but if I extrude from another place it snaps to it with no problem.
Then I tried to move a door opening to have it in-line with another door, but it will not snap. If I extrude from a vert, it snaps where I want it to snap within second.
My settings are: Snap on, vertices, closest, and snap onto itself. 
Am I missing some settings or is this a bug?
The problem is that you have proportional editing on, press O, or the blue dot at the bottom of the viewport to turn it off (see circled in red) 
You also might have forgotten to turn auto merge on (circled in blue), as you seem to have 4 vertices overlapping. To remove them, select everything (A) and use the Remove Doubles function (Press space and search up Remove Doubles).