A catalytic heater just requires gas, and something to light
it. Cheep tent units require you to light
them with a lighter. More expensive ones have a pizo igniter. The igniter is the push start button. When you push it you should hear a snap sound. These sometimes wear out, so you may need to use a lighter. It will make wouf sound, and you may see some flame. Then it starts producing heat.
You should be aware that these do consume air from inside your trailer, so leave a window open a crack, or something.