Wiktionary
vb. 1 (context idiomatic English) To understand or grasp. 2 (context idiomatic English) To be in control of, to have power over.
Usage examples of "have a handle on".
They need to be kneeding the same words for same things, need to capiche what they wanna do, have a handle on what secret rules say no 2 if you know, and a troo digging of the ground game stands on, air game breathes.
By then I should have a handle on the environment and I'll give an operations order.
I closed and locked the door, pocketed the bulky hotel key, poured the coffee down the kitchen sink, turned off the shower and left via the balcony door: I had to leave it wide open, held back in position by a heavy chair: for obvious reasons, few hotel balcony doors have a handle on the outside.
Something big was happening, and experienced as he was in the world of commerce, and now in the business of international transactions, he realized that he didn't have a handle on it.
We're supposed to have a handle on these things down at City Hall, but I feel like I'm boxing in the dark.