Click on the share page icon on any page (in page view or in a list view)
If its the first time using the slack share, we need to get some slack permissions from you to be able to share. Click the Grant Slack access button, this will redirect you to a slack page and get the required permissions.
Once you have granted permissions, this is the screen that will show going forward. Simply select the slack #channel or private @person you want to share the page with and click Share page
(It will then show up in slack like so)