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I'm pretty new to colimating newtonians as well, but here's my experience.
If the secondary is not too far up or down the tube (can you see the either end of the mirror on the long axis ?) if not, leave the centre screw alone.
To check the colimation on the laser, cut a Vee in a block of wood or use an engineering Vee block, mark a point on a wall 2 or 3 metres away and point the laser at it. slowly turn the laser in the block and see if the dot moves off the marked spot. If it does there are screws that can be adjusted to bring it back to centre. They are usually small hex socket screws down near the business end of the laser. Adjust by slackening and tightening (gently) 1/2 to one flat at a time.
Once the laser is lined up, slip it into the focuser and back the draw tube out a few millimetres. I've found that the ends of the drawtube bodies aren't always square and can "kick" the laser out of line if the draw tube is right in.
Look down the scope tube and see if the laser dot is in the middle of the primary mirror, most mirrors have the centre marked in some way. Adjust the 3 secondary colimation screws by slackening and tightening until it is (you can see the dot move so it doesn't take long to get the feel of which way to go).
Once this is done you can go on to the next stage of adjusting the primary until the laser dot returns back up the OTA tube and disappears into the hole in laser colimator from whence it came.
Hope this is clear. If not I have a doc here that helps, kindly provided by another member, I'll scan and post it if needed.
Bill
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