Control a TV with Harmony hub without activities in Lovelace

Hello everybody,
I have a question about controlling my TV via the Home Assistant, a Harmony Hub, and all about the Lovelace interface.

I have to say that I am new to the Home Assistant and have left the configuration of my Home Assistant to Lovelace.
Thus, I have currently created up to the basic files from the installation no other files (except the Harmony Hub conf).

I try now in the lovelace a button to turn on the TV set, but fail already at the beginning (Entity ?, Which card ?, etc.)

Does anyone of you have a detailed description of how I get TV on, TV off, the volume, a channel and even more stuff from a standard remote control into the Lovelace?

I currently use version 0.99.3

Thank you for any kind of help.

Greeting Christian