Arcade is a plugin you can use inside a DAW and also a standalone application, which can be opened like any other application on your computer.
Arcade requires an internet connection to get started.
Since DAWs provide the ability to record/edit MIDI and audio, it should be noted that standalone functionality is limited by comparison. You cannot record inside of Arcade directly, but you can preview, play and download Samples and Kits.
You can find the standalone app in the following directories:
macOS: /System Drive/Applications/Arcade
WIN: C:\Program Files\Output\Arcade