Go to Edit > Preset Manager (or you can open preset manager from the brush palette menu by clicking the small arrow at the top right). Scroll to the end of the active brush set, and click on your new custom brush to select it. Click on "Save Set..."
Note: Only selected brushes will be saved to your new set. If you want to include more brushes in this set, Ctrl-click on them to select them before clicking "Save Set..."
Give your new brush set a name like My Custom Brushes.abr. Photoshop Elements should save it by default in the proper Presets\Brushes folder.
Now if you want to add more brushes to this custom set, you'll want to load the custom set before you define your new brushes, then remember to save the brush set again after adding to it.
Now when you go to the brushes palette menu and choose load brushes, you can load your custom brushes anytime.


