A subscription product is the name we have given to the thing that defines what a subscription is (e.g. annual membership for an individual, for price £x). A subscription is what the member has (e.g. John Smith's annual membership subscription, which starts on 01/01/13 and ends on 31/12/15).
When setting up your organisation, you create subscription products (e.g. individual membership, group membership, junior membership, social membership, honorary subscription). The subscription products don't have to provide "membership of the organisation". You can also have subscription products for lockers, car spaces etc.
Your members can then purchase subscription products, for which they are issued with a subscription. You can also import your existing members' subscriptions.