How to create nice corners when building a wall with these concrete blocks?
You purchase corner blocks. Those are stretcher blocks for the middle of the wall, not corner blocks. A masonry supplier will have a variety of different shapes for particular purposes, one of which is corners (both full and half-blocks)
There are also special shapes for door/window openings (sash blocks and lintels), bond beam blocks for horizontal rebar placements, etc.
You might want to search on &quot;CMU construction methods&quot; (CMU is &quot;concrete masonry unit&quot; or the formal name of the concrete block.)