Loading Brushes in Photoshop is VERY easy. Just follow the steps below.
STEP 1: Unzip the .zip file you downloaded. Inside you'll find a file with an .abr extension (e.g. HW Vol.I-Palmtrees_PS7+.abr).
STEP 2: Open Photoshop and click on the Brushes tab in the upper right part of the screen. (SCREENSHOT)
STEP 3: In the drop-down menu that appears (SCREENSHOT), click Load Brushes and select the .abr file (the brush pack) from the dialog window (SCREENSHOT), then click Load.