The below guide is for quickly getting up and running sharing files using Beaker, a browser that can connect on the p2p web, and runs on Mac / Windows / Linux.
When we first open Beaker (or even just a new tab within Beaker), there is a "NEW+" button on the bottom right of the page. If you click on that, it allows you to create a new archive that can be shared on the p2p web using a "dat://" URL.
I'm showing that process in the below gif:
Because that gif moves by quickly, I'll just highlight the menu that pops up when you click on the "NEW+" button:
As you can see in the gif, if you choose "Empy project" (as I did), then you're given a new "Untitled" project. You can then name the project, and start dragging files into the project.
Note: you can continue to add files to this archive. It is simply a folder on your computer. In some cases you may need to hit "publish" in order for the changes to be made visible to others on the p2p web (still learning that myself :)).
Once an archive has been created and shared as above, others can view the archive contexts (effectively, making a local copy, which they also can re-share on the p2p web) by simply typing in the "dat://" url into Beaker browser on their computer:
Note: this step requires that the recipient was able to get a long "dat://" URL somehow. It might be nice to set people up on p2p chat, like Cabal, first, so that they can then share these URLs easily with one another :)