Adding flaps in either direction changes the chord line and therefore the angle of attack of the wing.

Flaps down = change in chord line to a higher angle of attack at the same airspeed, higher angle of attack moves the centre of effort (pressure) forward causing the pitch up. Flaps are used to A, slow the aircraft to enable a lower landing speed and B, give better forward visibilty (in full size) at the lower speed that would otherwise require a high nose attitude to keep the angle of attack in the range the aircraft can fly at the given speed. So left untrimmed the aircraft would initially pitch up but as it slows due to the increased drag of the flap/higher angle of attack the nose attitude would lower again to maintain the same airspeed. In fact youd probably need more power to maintan the same airspeed due to the higher drag.

Flaps up or ailerons up, lowers the angle of attack. With full span ailerons it basically destroys or weakens the lift meaning a higher airspeed is reqd to maintain level flight. High performance gliders use a very slight up or reflex, to allow higher speeds with less induced drag (drag as a by product of creating lift). Half span or tip ailerons with them up, destroys the lift only on the outboard section of the wing. On a any type airplane that is prone to tip stalling this means we can then fly slower with a lot less risk of tip stalling as the outer wing section is at a less angle of attack than the inboard section. You also maintain roll control using this method.