How do I connect two models to one PF motor?
As an addition to Ambo100's very nicely detailed answer, I'd like to add one more option: If either of the two things you are powering might suffer from friction (or perhaps a child holding it still), the provided solutions result in a lot of torque on the motor and axles, which in turn could lead to damage to those components (although LEGO motors are designed to switch off if put under too much stress). To avoid this, you could use a differential with in the white box in Ambo100's picture, like in this picture:



The motor would connect to the axle in the bottom right (with the big tan gear), and you would connect the Ferris Wheel and the Winter Carrousel to the left and right "output" axles. A differential splits the output power of the motor over the two axles and keeps the summed rotation of both axles constant even if one axle experiences resistance (the other axle would simply start rotating faster).