In regards to your first note, the apps that you develop with Honeycode are accessible through the Honeycode app (both on web and mobile). The links to download the mobile Honeycode app are available here: Download the Honeycode App
For the invitation issue, please ensure that the user you invited signs up for Honeycode with the same email address that you are inviting. Then after checking, re-send a new invite to the user to join your team.
Let me know if that helps and if you have any other questions.