In order to set up a membership fee, click on Planning - Subscriptions - Subscriptions and
Duration: select the length of the validity from the drop-down menu
Once you select a value for the duration you will be able to specify the length in a new field that will appear next to the duration.
Click on Confirm to save the changes.
If you click on Edit next to the membership fee you have created you will be able to add more details.
To link a card model, click on Edit - Other - Card Type and select an entry from the drop-down menu (they must have been added in the Settings first -> Card Models). When you sell this membership the system will automatically assign the card to the client.