Some apps have very few supplied strokes - you may have 10 or 15 items but that is it. There are no rules that you can't mix and match the resources from one app you have purchased with another (obviously, you can't commercial release items created from one to another but you can certainly use them in other apps to create new works of art / projects). Some apps make it easy to add presets, others actually make it impossible (such as the very basic apps). PSP / Photo-paint / Painter etc can all use the resources from PS and of course, vica versa.
Use them to create a dab for use in other applications
1) Select brush tool
2) Go to panel panel
3) Select required item
4) Make note of the brush size in the panel
5) Create a new document to that size (or greater if you wish to add additional dabs)
6) Set color to black via Photoshop toolbox
7) Apply dab
8) Save via the file menu via save / export or even save to web
Another option is now available via CC where the items can be extracted via the file menu extract assets command. With the CC, you can also now save any generated work to the CC library and use that in other apps of the creative cloud such as Illustrator (and hopefully some of the other apps at some point)
How to import ?? well that depends on the other application. If you are using PSP then simply select one of the tools in the toolbox and then display the options and select the menu command to create a stroke. If you are using it in another, you may simply have to add the genetated file (albeit PSD or PNG etc) and add it to a folder or perhaps open the file and then define it via a menu command or use an insert command - they are all very different. In some, the format may be precise such as only JPG or only PNG etc and all other formats are ignored.
You don't have to just export the basic stroke. Effects can be applied to the PS dab as well as layer effects and then export. Multiple strokes can be applied beforing saving the artwork for export to PSP, GIMP etc. You can also add to the artwork before any saving as well as removing parts from that item (perhaps using a shape set to the color of the background of the image). You can also just crop the image to select only part of that image to export.
Another possible option is to set-up a script that can run through a single image and apply effects and export and then remove that effect and re-apply another effect so a single item can be turned into 100s of different strokes (PNG files) with slightly different effects i.e paint daubs added, grain, stained glass, displace etc and of course, they also can have different effect settings so multiple grained dabs can be generated - again from a single image. Of course, not all of these will have any use but it is possible that a truly wonderful brush stroke can be generated via random combinations of effects and image. This can be run why you go and have a nice cup of tea or produce a new video etc in the background.
You can use a different type of effect: transformations. Simply re-size the stroke and then add in different locations on an image and then export that. You can also rotate / shear / warp etc the item and also store that as a new resource file (PNG format or otherwise).
The example below is a single dab from the collection set. The design was then saved via the file save command
Instead of a single dab, multiple items were applied in different sizes and in different locations before then selecting the save etc commands
You can always remove from any of the item - so in the above image part of the stroke has been removed simply by adding the stroke again in white (instead of black) and then that is exported to PNG via the file
You can also export them for use in other applications by applying various effects
You may be interested in flower brushes for use in PS and PS Elements, used on this page