Corners are used anytime you will changing the direction of your fencing. For example when running up the side of the property and turning a corner to run along the back.
Ends are used when stopping the fence. For example, when the fence is being placed next to a house or other structure. Do not count ends where you will be placing a gate or continuing on.
If you have sandy or rocky soil, the rebar stakes are the better choice. For areas with leaf debris, clay or standard soil the kinked stakes will work well.