Assuming the car is assembled -
Take off the spur gear cover
tighten the slipper clutch fully
With the car facing away from you, hold the spur gear and the rear wheel (nearest the spur)with your right hand.
Try to turn the other wheel
If you can move it freely your diff is too loose
If it doesnt move at all it is too tight
you need to turn quite firmly whilst holding on, when it turns very slightly with effort it is spot on.
As for the slipper.
A good starting point is to have 2 threads from the shaft protruding past the slipper nut.
turn on the car and transmitter (assuming it is ready to go)
Sit down and put the car on your lap facing away from you.
grip the rear wheels with your knees.
let the front drop down so it pivots between yor knees freely
With space in front of you pull full throttle and quickly let go.
If the slipper is too tight, congratulations you have a broken nose.
(remember to keep clear)
If the diff is too loose the car will twitch and squeal
you are aiming with throttle inputs to get the car pointing between 45 degrees nose down and level.
Thats about it. set the diff first then the slipper. Any changes to the diff tightness, you must change the slipper afterwards.
There are other methods so dont just go off my word
good luck