side slipping is crabbing. Same thing.

Rudder input noses the plane into the wind. Opposite aileron is fed in just enough to counter any rudder roll coupling, and to hold the upwind wing slightly down. This presents more of the plane to the oncoming airstream, slowing it, allowing it to sink, and prevents it from drifting sideways with respect to the ground in the crosswind.

Rudder is like the other surfaces. You don't just go out and "learn rudder" any more than you spend flights "learning elevator". Do the same thing as you have with your other control surfaces, see what it does and how you may be able to use it.

J