Shock Rebound?
 

Is it important and how much do you have?

Full, half or not at all?

What purpose does this serve on the car?

Less Gripy and bumpy tracks more rebound?, Hi grip and smooth no rebound?

When building shocks I always aim for around 5mm of rebound when you push the rod all the way in,
I would never want more than that as I find the car doesnt handle aswell or seems inconsistant

rebound just makes the car unstable so i have none

Rebound is caused by pressure in the shock, pressure in the shock is bad - causes blow out of O-rings. If you can't press the shock rod end right up to the shock body, then remove bleed screw and relieve some pressure.

I always hold the rod end at body while putting the bleed screw back in. Result is usually 2-3mm of rebound. The effect is nothing, may as well be none, the important factor is damping.

When I'm filling my shocks (with bleederscrew)
there is some thing wrong.
The shaft pulls it self back in, how can i solve this?

As long as both sides match, it doesn't matter.

The shock is about displacement of the oil to compensate for the shaft as that goes in. Its bad to have too much pressure, but stop the rebound pressure and it'll suck the shaft back in from full extension.