Imagine your dining room table is covered with books because you are researching something. Then you need to eat dinner, so you find a box to hold the books temporarily. After dinner, the books can return from the box to the table.
The table is RAM, and the box is the Page File.
That's pretty good, but a better analogy might be...
The RAM is like the table. That's where you do the "work" on documents and items.
The filesystem on disk is like the filing cabinet you have next to the table. Inside, you have a variety of files inside folders, all nicely sorted (with an index pasted to the outside). But, you can't really "use" the files while they're in the filing cabinet. You have to pull them out (open the file) to use it.
The Page File is a "junk folder" in the front of that filing cabinet. It is for the stuff you're still working on (they're still "open") but for which you've run out of room on the table. You can't really work on them from inside the folder, but it is a place to stick stuff when you run out of table-top space, without having to "file it away" (close the files) into the full filing system.