Put voltage on the primary of a transformer and a voltage appears on the secondary X turn ratio.
Current from a secondary must come from the primary. (turn ration)
Put a load on the secondary and the load appears on the primary. (turn ration involved)
A transformer is much like a electric motor turning a electric generator. Start out with 110 volts from the power line, that powers a motor that turns a shaft that turns a generator which makes 110 volts. ( or it could make 12 volts for your car) If you put a load on the generator (light bulb) the generator gets hard to turn. The motor must work hard. More power comes from the power line to run the motor. So turning on the light bulb (load) makes more current go into the motor.
I see this may have changed to a new, but adjacent subject. But, the best-designed transformers, have small mutual inductance. You'll see more of the mutual inductance effect the poorer the transformer design.