Getting started
The main feature of the companion Slack app, flagging messages for possible leeks, uses both message reactions and message shortcut actions.
Via message reactions
React with the :leek:
or :leeks:
custom emoji on any channel where the app currently resides.
Via message shortcut actions
In any message, hover over the message on the desktop and click More actions
or hold it on mobile to show the options menu then select More message shortcut
At the shortcut selector, search for Flag as leek
from the Hack Club Leeks app (use the production one and not the development instance).