Depends on which kit you have m8 most just need the diff box opened up and add some blutac,balled paper or if u want it perm locked glue so the diff cant rotate against it self they move the same way ie forwards

eg when one wheel is lifted in a corner the power is moved to the wheel on the ground,as you turn the outside wheel has to stay a higher speed (more rotations) to the inside wheel to stay straight without spinning out etc

locking diffs is great for drifting as both wheels move at the same speed...but it sucks for racing tbh too many spinouts.

most lock the back more than the front it depends mostly on your style and what tyres you run.