hi slice, they are talking about the locking screws for you primary mirror. at the bottom of you OTA there should be 6 screws. 3 of these are for adjusting the angle of the primary mirror during collimation and the other 3 are to lock it in place when finished. undo the 3 locking screws on the bottom of the OTA before collimating and do them up when finished to lock the mirror in place.
ps, dont do the locking screws up too tight.