1. Go to download the brush tool that you want to add on
2.Open Photoshop. You don’t even need to open up an image. Simply open up the program in order to install your brushes.
3. Press B, or click on the Brush tool, to bring up the brush bar on the top of the screen. There is a bar on the top of the screen that changes depending on what tool you have open. Simply press the B key to switch to the brush tool.
4. Click to open the Brush preset picker => Load Brush then It can help to have a Finder or Windows Explorer window open showing the brushes file that have extension .ABR=>click to open it