There are two options used to allow access to your app: Permissions and Rights.
Permissions - This refers to User Permissions: grant users the ability to access, manage, and customize your custom app, as well as the app's Rights as explained in the next point.
Rights - This screen allows you to enable Rights in your custom app, which are disabled by default. By enabling a Right, you will be able to select it within the app's User Permissions as explained in the previous point. Note, however, that a Right has no intrinsic functionality. If a Right is enabled, it will not work without customizing the app.
For more information on what each permission does, please see Permissions and Rights.