Four bar linkage (grey pedal, green conrod and pink crankshaft) is used to convert pedal oscillation into rotation of propeller like in foot powered sewing machines.
Turn the pink wheel clockwise a little at starting going forward if the linkage is in its dead position.
Blue handlebar is for controlling the blue rudder.
Only lower portion of the pink propeller is submerged in the water so the propeller thrust does not make the boat go straight. Use the blue rudder to keep the boat going straight.
Adding a second coaxial propeller of opposite blade direction and opposite rotation direction can maintain the straight going however it is too complicated.