Why is a pair of scissors considered a first class lever?
Scissors are levers because, the fulcrum is between the applied force and the load. The load are the blades. Your hands are applying the force. Scissors are the first class levers.
Because your fingers are on the opposite side of the fulcrum to the load?
Because the load is on the opposite side of the fulcrum as the effort. Other examples are see saw's, rakes, and even home-made spoon launchers!