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There are two sets of knurled slotted head screws. 

Three of these screws have heads ½” in diameter. These are the collimation screws. Confirm their identity by looking for the springs they hold against the back of the mirror assembly. They are used for tilting the main mirror to collimate your scope’s optics. Instructions to do this are found elsewhere in the Celestron Knowledgebase and are virtually the same for all Newtonians - Dobsonian StarHoppers are one type of Newtonian. (If you want to collimate your StarHopper, look for the collimation instructions under the Advanced GT Mount FAQs for the Advanced GT reflecting telescope.)

The narrow, ¼” knurled slotted screws are the mirror locking screws. These screws are used to lock the mirror in place to either better maintain collimation or for safety during travel to prevent excessive mirror assembly jiggling.

To use the locking screws, turn them inwards until they are in contact with the mirror assembly and preventing its free movement.

Be sure the locking screws are turned outwards and allow free motion of the mirror assembly before collimating your scope.