Have A Handle On Meaning

(idiomatic) To be in control of, to have power over.

Example:   To work efficiently, it's important to have a handle on the procedures involved.
2003, Tony Hillerman, The Sinister Pig, ISBN 0061098787, page 36:
  But the other three problems had all grown out of assigning jobs to people he had no handle on.
2011, H. Henrietta Stockel, Drumbeats from Mescalero, ISBN 1603442308, page 82:
  We don't have to report to them anymore, but they still have a handle on our Justice Department and the police.