Oh! Most of them are tilesets, if you go in the chipset folder the tilesets should be in there however a few,such as the chrono cross maps are pictures bwahahaha.
Im not entirely sure how it works completely but I have the gist of it. You first make an empty map, make sure the width and the height of the map mostly match the width and height of the picture you want to use as a background - I think and then it'll work. You open up your map and check the parallax background checkbox and set what picture you want to be the background as, then when you close out of it the picture should be on the map, for me there's a lot of trial and error I usually get pink screen of DOOM, and it doesnt display the picture correctly - so you gotta make sure the sizes match kind of.
Im lazy so what I do is when Im too lazy to make a map or a tileset I take the picture, slap it on a picture I know already works (there located in the Panorma folder) paste over it with my new picture, and re-name it, then I put the new picture in the Panorama folder, then when I go into rpg maker vola, I can load it as a parallax background to my map.
What sucks about this, though its a time saver, there's no solid 'cant walk on water' etc, so you have to use events to make sure the player doesnt walk all over the ocean in say the homeworld I made for example XD.