How does a hot air balloon fly?

How does a hot air balloon fly?

Today we were told to go on wonderopolis and learn about something and make a blog post. I have wanted to learn how does an air balloon fly. I have done 5 facts about it.  Here is what I have learned:

1. it flys by fire 
2. it flys by gas
3.  the heated air causes the balloon to rise because it is lighter than an equal volume of cold air.
4. Hot air is less dense than cool air
5. A hot air balloon uses a burner to heat up the air inside the balloon.

My next step is to try and learn about something else