Brush ( extension .ABR ) is tool that already have a shape ( like animals, Trees, Buildings, etc. ) and only its size that can be adjusted. you can download it free from the internet. after you download and extract, copy or move the -----.ABR into adobe files -> Photoshop -> Presets and paste.
this one of my creation using brush
1. Click file and new. Set anything you like
2. Click Brush tool and choose brush in the icon.
3. Choose brush anything you like. for me crispy crack brush :-)
4. Go to icon and choose Gradient fill and Black & White. set anything you like
5. Put another brush on it and you have this effect :-)