Both answers are totally valid methods, I use both quite a bit but there is a more dynamic way of doing it that I use when it’s orthographic snapping.
It’s a similar method that @mitchino has outlined using just the Move Tool, Axis and Snapping.
Axis manipulation is the key:
- with the Move Tool and Snapping active, select the object you want to move.
- On the axis handle you want to move along, Ctrl+Right Click it and release.
- The Axis handle will now be moving with the mouse but not the object, you then move the mouse over the edge you want to move (so you see the snapping activate).
- Left Click and hold at that snapped edge, drag over to the target edge until it snaps and release the mouse.
Sounds a bit convoluted, but once you’re used to it, it’s quite useful.
Here it is in action:
Here it is in 3D with Polygon snapping:
For the original example, you’d want both Edge and Vertex snapping: