Cassegrain telescopes allow only the secondary mirror's angular alignment to be user-adjustable. The primary mirror, corrector plate, and back axis are fixed at the factory - hopefully already accurately collimated when you receive the telescope.
With the Howie Glatter laser collimator inserted in the eyepiece holder, collimation can be accomplished by adjusting the secondary to align the laser dot ("impact") as close to the center as possible. The laser's beam can be seen from the front of the telescope by looking through the corrector plate as a result of double reflection in the primary and secondary mirrors.
However, it may be difficult to see the collimator face because the view can be restricted by the baffles in some telescope tubes. If so, this side cut-out adapter tube makes it easier to see the collimator face at the back of the scope.