Just download the DMG and double click it to mount. Drag the Bunch icon to the Applications folder. You can then launch Bunch from your Applications folder. (Or with Spotlight. Or Launchbar. Or Alfred. Or the command line. Or AppleScript…)
You’ll probably want Bunch to stay in your Dock for easy access, so go ahead and launch it once, then use Preferences->Launch at Login to add it to your Login Items.
See the configuration section for instructions on personalizing the setup. Use “Reveal Bunches in Finder” to go directly to that folder and start editing/adding Bunches.
To use some of Bunch’s features, you’ll need to give it Accessibility permission in System Preferences. Open System Preferences and go to “Security & Privacy,” then select the “Accessibility” tab from the list on the left. Click the lock icon in the bottom left and unlock the preferences with your system password. Use the (+) button to add Bunch to the list from your Applications folder, and ensure that the checkbox next to it in the list is checked.