In the Projects Dashboard, click on Join a Project button and Paste the 5-word secret you received from the project host.
When you are joining a project,at least one existing peer from that project needs to be online in order for you to sync to that project.
If everyone is offline, the project will be added to the project queues until you and at least one peer are online so that the project can sync.
Once you both are online the project may continue to take one or more minutes to synchronize and to display itself as available in your dashboard.
In order to be able to collaborate on a project, you and the other project users must be on the same "major version" of Acorn. This means that the first number in the Acorn version code, such as the "5" in "5.0.1-alpha", must be the same.
E.g. Version 6.x.y WON'T synchronize with someone using Acorn version 5.x.y.
After you enter the 5-word secret to join a project, Acorn will look for any online peers for that project and until it has found at least one to sync with, it will indicate that the project is waiting to sync.