After logging in onto your crm account you will need to locate the subscriber panel, which is found on the left hand panel tree. Click on it and then click on New to add a new subscriber.
You will get the following page with will have fields you can fill in and save. If you have the details of the subscriber, please fill them in. The minimum amount of information you need to create a new customer/subscriber is their first and last name and email address.
After hitting the save button you will see the details populated on the fields, with the subscriber being in the system.
Furthermore if you are looking for a subscriber, you can find them by going to subscriber, then find and searching their details by any of the listed field options.