The knob on the top , that is on the shock resevoir is the compression adjuster . Turn it in (clockwise ) and it should make it stiffer , turn it out makes it softer .
The rebound adjuster is on the bottom clevis of the shock shaft , turn it in (clockwise ) and it will slow down the rebound , turn it out and it will speed up the rebound .
Now if there is no oil in the shock the adjusters will do nothing , and if you push down on the bikes seatr and let go it will spring up really fast , to the point that it will almost pull the rear wheel off of the ground !
We can rebuild it .