How To Use SnapShots In Photoshop Tutorial
Photoshop snapshots - Window menu and history
You get the standard list of all the various things you have done with the current document such as effects applied, adjustments added, layers added etc but at the top of the panel, you get your special entries that you have recorded via the right side menu commands.
You also get another panel of commands via the options right side menu commands where you can set up the recording for the initial opening of the document, for each and every time you save the document etc. The initial entry is one of the more useful. The save option less so now as you have version history with the application.
You have applied a load of effects or brush strokes or gradients etc, go to the right side menu and click the new command and you will see your entry appear at the bottom of the 'top part' of the panel (it is split with those entries along with the standard applied effects etc). When you are saving it, give it a decent name as well as select whether it is the full document, the merged layers as well as just the current layer (which is also useful). It should be noted that the result is always a pixel layer so if you record some type or shape, if you restore it later via the fill command then it is restored as a pixel and not a vector.
You can select the entries and delete them
You can select an entry and then create a new document from them via the new document right side menu command
Sadly, it does not save the entries when you save the document. If you want to do that, you will have to use version history to the cloud (on the video I mentioned that it is saved, that appears not to be the case ! which is just plain odd as it would be very useful if they were)
Set a history state (left side) in the panel before you run the fill such as one of the special recordings. Select the content as history and apply. You can set the blending mode, opacity etc but note that it is always a pixel layer
History / Art brush
You can also select one of those entries in the panel and use them with these brushes and vary the size, style applied etc