Hi Diane. "Public Sidebar" is just a thing I put together so there's no "beginner information" or official docs on it. But do note that in the menu showing in the sidebar there, there is some guidance.
But, yes, in the ".../main" you should simply edit it to state your own domain so it applies there instead. Take care to use the same format, e.g do not include the "http" at that place.
If your unsure, just install it into another copy of your TW and experiment.
Maybe that is enough of a start to get things working for you. Otherwise, the main thing to understand is CSS because this is what is used to style things.
<:-)