Find a brush you like!!
Click on Free Download
Click on your finder (happy blue square face)
Go to your download folder
Double click on the brush ZIP to open the folder
double click on the ".abr" file
The brush will automatically be added to your brushes in PS
On a blank layer, draw/ write/ design your brush
Use the rectangular Marquee tool to select your entire image
Go to Edit > define brush preset
Label your brush and click ok
Your brush has been added to the bottom of your brushes in PS