To check the broadcasters available, click on the antenna icon :

Here you have a map of all the broadcasters. At the beginning you will be able to work with only a few:

To unlock more broadcasters you will need grow your fame level by gathering XP points from recording videos or in gatcha Bonuses.

You can turn on the broadcaster with the help of the slider:

Running a Broadcaster requires Staff, each broadcaster has a different requirement. If you run out of Staff, you can reallocate some from other broadcasters or skills or hire some more from the HR Department :