In orde to collimate your Newtonian telescope, please follow these steps:
1) Take your telescope Newton and remove the front cap
2) Place the collimator in the focuser, then turn the switch to turn it on.
3) Look at the red dot position on the primary mirror. Usually at the center of the Newton primary mirror there is a black circle to help you understand exactly where the center is: if the laser point is not in the center, it indicates a misalignment of the secondary mirror. Then use the secondary mirror collimation screws to perfectly center it.
4) Observe the red dot position on the reticle of the collimator. If it is not centered, it indicates a misalignment of the primary mirror. Then use the primary mirror collimation screws to bring the red dot at the center of the grid (on the hole).