The Hindenburg sessions are cross platform, so you can begin working on a windows computer and finish it on a Apple computer.
To share a session on dropbox, you need to have a shared folder.
Save as - to dropbox. This will save the session file (.nhsx) and the Files folder that contains the content.
Synchronize the dropbox folder on the computer you would like to open the session on.Click in the .nhsx file to open the session.