Affinity Photo snapshot feature captures the current image. You can create multiple entries to the snapshots panel (found in the view menu and studio). Document menu and then add command (first in the menu); to restore, use the restore option and in this case the image will be restored to the version you select, as there maybe multiple entries there. The key menu is document and 'add' and 'restore'. The history panel is useful for keeping track of a whole swathe of commands but this feature enables a quick add and restore to any point and is clearly defined hopefully by giving it a sensible label. You can also use the add and restore feature found on the related panel. The panel also offers the additional feature of being able to delete the selected entry
Go to the document menu and click add and then give the entry a sensible name such 'working with Gaussian blur and deform' etc. If you wish to restore, go to the document entry and select that entry from the list. If you are using the panel, select the entry in the panel and then click the restore button (which is the first at the top of the panel). The restore brings everything back to as was at that point such as the layers, settings etc
You can also go to the layer menu and use the new layer from snapshot command and this will just return a single layer image (it does not restore the layer structure etc, just what was the image at thew time). This layer can then be used as a great source for effects, blending and much more.
If you wish to keep all your saved entries when you come back to the image, you will need to go to the filer and save command and save it in afphoto and when you re-open the application you will find all the entries are returned to the panel
You can also go to the panel and click the fourth button at the top of the panel and create a new document based on the selected entry. The new document created will have all the layers (shapes, etc) as was at the time of the capture
You can also make them from all kinds of things via the little + in the panel. If you scale an image and then you can capture that. You can rotate and scale and crop and capture that. You can create a pattern and capture that. You can add effects and image adjustments and add text and so on and all can be added to the panel. Once you have everything, you can always just go to the layer menu and new layer from and you will have a long list of different filter / adjustments / crops / effects / adjustments etc and you can then build up a quick contact sheet of your progress with the work or an idea sheet etc