To import Photoshop brushes, you need ABR files. The expected format for the strokes is ABR. You can find zillions of ABR sets on the web, free as well as full priced, commercial as well as persona use. All are accessed via the tools in the toolbar such as the paint, clone, art history etc
Brushes import / accessing has changed with the most recent versions of the application. Go to the tools and select any of the painting / blur / smudge tools and others. Go the brushes panel and then go to the right side commands and use the import command and you can bring in many sets or just a single set
One you have brought them into the application, you will notice that they are in groups now and the groups are based on the original file names. You can remove the grouping if you wish as well as move the presets from that to another section or just delete any of the entries that you don't want.
There is now no need for an install folder. I would suggest however that you keep all your files in single location as that makes it so much easier when you come to upgrade your version or if you want to move them to another machine etc. You may like to keep them all on a secure cloud server and then access them there and bring them into the application as you need them. The more of the presets you add, generally the more resources of the machine are used up and the harder it is to find the resources
If you are using an earlier version of the application, you will have a right side menu of the panel and you can select the brushes file from there or use the load / replace commands. In the previous versions there was also a preset manager in the edit menu and that could be used to load the files.