Have you gone through our getting started guide here: https://trello.com/en-US/guide
It could help uncover the problems you may be having.
I'm not sure why they are unavailable to communicate, but if you invite them to a board and they sign up and join your board, they should be able to leave comments and make new cards on your board.
Hello Community! My name is Brittany Joiner and I am a Trello enthusiast and Atlassian Community Leader. I'll be sharing with you a series of videos with my top tips on how to best use Trello...
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event