First, seat the screws and give them a couple of precursory turns.
To attach your motherboard to the case, screw it in. First, seat the screws and give them a couple of precursory turns. Then, proceed in a star pattern, tightening each screw a little at a time. Don’t go wild while tightening, as you might damage the board. You only need enough torque to hold the board in place without it wiggling.