On this tutorial you will learn how to open a image on photoshop and convert it into a brush, aka how to install one image as a brush.
Open the brush image pack on Photoshop
(Go to File - Open - find where you saved the image on your computer and open)
Pick the Lasso tool
Click and drag the mouse around the brush you want
After the brush is selected, go to the menu "EDIT"
and choose "Define Brush Preset"
Just type any brush name and click "OK"
Your brush is now READY under your brush tool!
Create a new document by going to File - New - Press OK
Select the brush tool
Now you can just click around like a normal brush.
If you right click on the picture with the brush selected
you will see your new brush there.
Repeat with other images you'd like.