Square Zero to Square One:
Slack is a painful example of the too common problem of not providing a clear path for a complete novice to get from knowing nothing (Square Zero) to achieve the absolute minimum use. In this case, setting up a project channel and then adding members.
Having a bunch of sales stuff about all the great features is worse than useless. Once the project is running, they can learn the fancy features.
You must get the newbies from square zero to square one.
Enjoy, Tom Riley, Born to Storms AI