How we transmit to satellites?

Usually there is a ground control center which transmits to the satellite and controls it's actions, receives it's data and adjusts it's orbit. Using satellite dishes and antennas we receive and transmit to satellites  radio waves.

Maybe here you can find some more helpful info. 

The transmission itself uses electromagnetic energy which travels in the form of a wave. Different frequencies are used for different types of transmissions and the information transfered is received by the satellite using powerful receivers.

On the ground, as fish mentioned, we have stations that are responsible for controlling the satellite and they do so by sending information which is then encoded by the satellite into a certain process. 

All the best