Select brush image in Photoshop and edit menu and define brush and then give the preset a name. The resources is then added to the current brushes panel. Use it with many of the tools in the tools panel. Give it a name, makes it easier to search for - something that I rarely remember and ignore my own advice and the application does have a great search feature to find those presets but it does need to have a clear and easily searchable name.
Select the custom shapes tool and Set the color to black. Apply custom shapes (such as type as a custom shape) and select and edit menu and define command. Perhaps change the color and go for some different gray designs.
Custom shapes can be used over and over to create unique new designs, you can also combine the vector artwork with effects, you can distort them, use them with transformations, different colors, different style effects, change the opacity, use different blending modes, add filters to them such as blurs and wave filters etc and more to create more and more unique resources to be used as strokes
Open an image such as a public domain page scan and edit menu and define command and give the stroke a name. Of course, you can always start from a scan or a scan of a sketch etc, that is another great start point for any number of strokes (I have used public domain images in the past, mainly stuff from the 18th century to make really certain that they are public domain). Another key thing to remember with artworks - they are gray scale. You can either start working with a gray scale or you can use the powerful black and white adjustment tool (image menu) to turn any color image into the perfect image to capture. Of course, you could just keep the original image as a color image or use an adjustment layer to change the color of the stroke to gray scale. You can also apply effects to the designs and then store them as a new stroke.
Another option, and one I often use is to use a PSD document and create them on layers and then you can create many variants of the same artwork which can then all be preserved in the PSD for future use and manipulation. Saving them in PSD format also means you can use the live effects and live layer effects and save those with the strokes for future changes. Remember to save the file otherwise you will have to re-create the design at a later point. Also if the work is saved as a PSD file you can always open the PSD file in other applications and re-work the artwork with other tools and use those as presets (strokes, pattern tiles etc)
With recent releases of PS, you can now save the artwork created in the creative cloud libraries panel. This is useful as the libraries panel can be used as a massive store of any of the developed or part developed presets. You can also be sure that the items are saved securely on the Adobe server. You can then re-use them at any point in the future and continue to work on the items or perhaps add additional elements or remove parts of the stroke etc.
With the define command you have not saved a complete tool, only really a dab. You can now go to the panel and set various shape dynamics, scattering, texture etc. Note: this is only accessible if you are selecting a tool found in the toolbox. Set different spacing, set various scattering settings and then go to the right side menu of the panel and select the new preset command.
The preset now has all the settings (marked by a check box) and can be recalled via the preset panel. I, personally, have always found it odd that there is no update preset command so any changes to the preset - such as adding texture as well as adding dual option can be updated. The only option seems to be to add a new preset and then delete (if you wish) the old one
You can go to the panel and select some strokes and then go to the right side menu and export selected command and save it as an ABR format. The ABR can be accessed in Photoshop as well as Affinity Photo as well as Clip Studio Paint and many other applications
Well, that is a totally different thing. You need to know what you are creating them for. If you want a star burst scatter effect or explosions or splatters, it is no use creating a tool made out of pandas. It might be a great panda preset but it is going to be no use for star effects. Good ideas and good source material and you should be able to make wonderful new painting tools. Personally, the best tool for creating and making the tools is Illustrator as you can create a new infinite number of excellent vector artworks which can be then used with any size of preset. My favorite tool to create presets has to be gradients as well as contour effects. Illustrator also comes with some truly excellent tools to make them such as the VectorScribe plugin set from Astute as well as MirrorMe as well as the excellent Art Blue plugin set from Amazon Canvas.
Gradients are an excellent source for new presets and the defining of those presets. The best gradients are ones with transparency in them especially at the two ends of the gradients. To do that, select the gradient tool and then click the gradient editor at the top left of the application and then edit the current gradient. Select the end stops and change the opacity to zero for those. It doesn't matter if the gradient is colorful, the preset will be saved as a gray scale image. I always find the best gradients to add are radial designs so select that type and then apply the effect. You can then build up a complex set of images across the document and you can then go to the edit menu and define command