Users with Admin rights can set folder Permissions from within the folder settings. By default, users have access to all folders upon creation.
Click on Permissions and a dialog box will appear. On the left side it will list all users that have access to that folder. If you want to remove access from a user for that folder, click on their email in the Users WITH Access column and then click the button to move their email to the Users WITHOUT Access column. Click Done to save your changes.