1 - Start Adobe Photoshop
ABR files can only be created from Photoshop, this is why you need to start the application to export/create a new ABR file.
2 - Open the Brush window
Go to Window > Brush or right-click in an existing document with the brush tool selected to open the Brush Window.
3 - Select the brush presets (and groups) to export
Press and maintain CTRL (Control) to select the group and the presets that should be saved in the ABR file.
4 - Export to an ABR file
Open the settings menu of the Brush Window and select Export Selected Brushes.
A file dialog will appear asking for a location and a filename to give for the ABR file that will be created on the disk.