Each button does say it's usage when you hover over it, and is also listed on the commands page,but the brief explanation is:
You use the buttons to set permissions to a user account, green means allowed, red/orange means disallowed.
This allows people to en-queue songs
This allows people to skip the current song in the queue
This allows people to use the admin queue.
This allows people to use the playback options
This allows them to stop/start the bot (MUST HAVE ACCESS TO THE INTERFACE)
This allows them to edit the bot settings (MUST HAVE ACCESS TO THE INTERFACE)
This allows them to login, giving them interface access.
This allows them to upload files (either from interface or !ytdl)
This allows them to delete files (MUST HAVE ACCESS TO THE INTERFACE)
This allows them to create/delete a playlist (MUST HAVE ACCESS TO THE INTERFACE)
This allows them to edit a playlist (MUST HAVE ACCESS TO THE INTERFACE)
This allows them to edit the bot instances (MUST HAVE ACCESS TO THE INTERFACE)
This allows them to edit user accounts (MUST HAVE ACCESS TO THE INTERFACE)
If you need any more assistance, don't hesitate to ask!