How to create new brushes from Photoshop patterns tutorial in CC 2017 2015 etc
This tutorial is based on the PNG files on this site, similarly works for other PNG etc files. Chevron / angled patterns and colorful seamless tiles are used in the examples
Open the PNG file or use the place command in Photoshop - that is the first thing, once loaded it can then be manipulated in a number of ways such as adding effects or using it on channels etc - as with most things in PS, there are 100s of ways of creating new and exciting brushes
Open PNG file and go to the edit menu define brush. You can define the entire file or just use the rectangular marquee and then select part of the artwork and define that as a new brush.
Once you have a brush defined, you can also go to a new document and then apply that multiple times, perhaps mixed with effects etc, and define that as a new stroke as well. That is a fairly basic way of creating infinite numbers of new brushes based on patterns designs however you can go even further by using the patterns with features such as fill content and that can also be defined as a new brush stroke
You can also open the PNG file and then define it as a pattern via the edit menu. Once it has been defined, you can now use the pattern via the edit menu fill command and select pattern (and perhaps use it with the random fill or symmetry options to create even more interesting designs. If you create a layer then you can also add content to that and then use the layer menu and layer styles and pattern overlay (and you can also use the patterns as wonderful brush textures which can be permanently incorporated into the art) and that can also be quickly used as a great source for new brush strokes by flattening the artwork and then selecting part of the design or all of the pattern fill and then use the edit menu define brush command.
For myself, the best approach is probably the fill content which can be made of a solid color or gradient or pattern. The pattern can be scaled using the fill content layer scaling and re-colored using adjustment layers etc and the result of that layer can also be flattened and then selected or part selected and then edit menu and define brush to save the pattern as a brush.
The pleasure of the fill content is that is a layer and multiple layers can be generated and blended using blending modes such as darken and lighten etc to create all kinds of unusual designs which can be then flattened and again, selected and defined by the edit menu and define brush command.
Another good thing about a fill content layer (once it has been rasterized or turned into a smart object as the fill content layer can't have a layer mask in its default state) is that you can always add a layer mask to it via the layer menu and layer mask and then in the layer panel, you can modify the mask so the edges of the image are faded so you won't end up seams in the brush stroke (if that is not an issue then you should not worry about it). You can also use brushes to create the layer masks such as overlay and textured brushes and plus / cross themed artwork brushes and polka dot and spotty brushes as well as layers for Photoshop, psp, Affinity Photo etc to create many different kinds of layer and resulting new brushes from patterns
You can find many other tutorials such as how to create a random color grid Photoshop pattern and how to create a rectangle pattern in Photoshop tutorial using lines and random fill script and how to make color triangle patterns in Photoshop and how to use Photoshop keyboard tool shortcuts for quick access to tools