Important note: When adding New Users they by default have no access to any folders.
In order to protect the confidentiality of all of your files, New Users are defaulted to zero access. Access needs to be proactively given to specific Folders. This can be achieved in two ways.
1. Make them an Admin for the account. This is for super-users. Under Users: Settings, if you set their Role to Admin, they will have access to all of your files automatically (be careful!). You can do this by clicking on the box that shows their Role.
2. Set their Permissions. This is more common. Under Settings: Users, you'll see next to their email address a Permissions box. If the box says None, it means they won't see anything. You'll need to click on the box and choose what Folders (or Tags) they should have access to.