Mattermost integration

a customer of me asked me if I could do a Mattermost integration.
I was willing to do this, but I stopped with this action because of the following info .

I am an administrator of Monday. Will this integration be for all boards in monday of our company… Will it read all information of all boards? I only want to use it for that specific customer board.

Can someone explain to me how the integrations work.

Kind regards,