Get/have a handle on somebody/something
Definition 1 of 1
Pro Tip 1/3Metaphorical Grip
Imagine physically grabbing something to remember this phrase means understanding or control. 
She got a handle on the company's finances within a week.
Pro Tip 2/3Control Nuance
Remember 'have a handle' suggests maintaining control, while 'get a handle' suggests achieving it. 
He needs to get a handle on his temper.
Pro Tip 3/3Learning Context
Use the phrase when discussing mastering a skill or learning how to manage a new situation. 
I'm still trying to get a handle on French grammar.