This toilet seat has hinges with fold-down
covers that conceal the screws.
They supply foam pads that stick to the
underside of the hinge and help prevent the seat from wiggling
and becoming loose.
The seat was placed on the toilet and the nylon
screws were inserted in the holes.
While holding the plastic nut, I turned the
screw with a flat blade screwdriver.
Then the covers just snapped in place.
That's all there is.
Note: Replacing an old toilet seat can pose problems
because some older seats use brass screws which typically corrode
after a few years. Often these screws must be cut off with a hack
saw or broken off with pliers, as the nuts can rarely be loosened.