Connecting Slack to Windmill will not give Windmill access to anything. In order to pull data into Windmill, you must add the Windmill app to your desired channels.
Navigate to the channel you want to link to Windmill and tap the name of the channel or the channel members on the top right of the window.
Once you see the list of members you can tap the "Integrations" tab.
On the "Integrations tab" you'll see a button to "add apps".
Search for "Windmill" and you can add the app directly from there.
Click here to connect Slack to Windmill.
NOTE: Adding Windmill to a Slack channel, will notify the members of that channel.