Answer:
The simple answer is experimentally. The first regular public broadcasts began in January 1929 when the BBC began transmitting programs from their London studio. All use of television before that time was limited to demonstrations and test broadcasts.
Notable dates are March 1925 when John Logie Baird demonstrated the first moving images to be carried electronically. The demonstration was held in Selfridges, a London department store. It was this system that the BBC used for their first public broadcasts four years later.
In 1927, Philo Farnsworth also demonstrated a television system of his own in the US. He developed the system to show off the first fully electronic television system in 1929.