To open the folder settings, just select a folder and on the workspace header click the gear icon.
In the folder settings (accessed when editing a folder or creating a new one), you can customize your folder name and visibility:
General: Choose a name for your folder
Members: Manage folder visibility by adding and removing members. When you add a member to a folder, that member’s access and role permissions cascade down to all the folders, projects, and sprints within that folder.
For example, if you add Ryan to a folder that contains two projects, he will have access to both of those projects. Of course you can overwrite any project’s permissions to remove Ryan or change his role specifically for that project.
What members can do on a folder and its nested folders, projects, sprints, and tasks is defined by the role(s) each member belongs to.