Manual piloting is a generally a myth. I heard it when I started out too.
While there are a few scenarios (trying to hang someone up against a station who is orbiting you, pulling someone into a gate, etc…) they’re pretty rare.
Agility allows you to turn faster, which increases angular against an orbited object (so it can be used to help you get under someone’s guns).
Also nice for align times on gates… let’s you hop faster.
Selecting maneuver is functionally mostly confined to these options:
Fly straight line in space
Sit still
Orbit a jettison can
Orbit target at selected range
Keep target at selected range
Approach target.
Picking the one of these that gives you the most substantial advantage is trick, and requires some thought.
Read this tutorial, let me know if you have questions.
Tutorial on mechanics
After chapter 6, I talk about selecting maneuvers. Read it.