a grip on
*a grip on something
1. and *a hold on something Lit. a good grasp on something. (*Typically: get ~ have ~ give someone ~.) Try to get a grip on the ropes and pull yourself up. You should get a hold on the knob and turn it firmly.
2. Fig. a thorough knowledge of some topic. (*Typically: get ~ have ~ give someone ~.) I need to have a grip on the basics of accounting. Try to get a hold on all the facts first.