General

This tab contains the main attributes of a tangible product. A tangible product is usually a physical item, that you have to keep in stock and ship to your customers when purchased.
Service, subscription, downloadable

All of the fields have the same meaning as for the tangible products. The only distinction is that Service, Subscription and Downloadable products do not have the fields that are related to physical items (backorder controls and weight, for example).
A subscription product is designed to sell subscriptions (or memberships) to other In-portal sections or modules. For example, if you want to have separate News sections, a free one, and one for paying members, you can use the subscription product to sell the membership to the paid news section.
A downloadable product is designed to sell any electronic products such as software, e-books, mp3 files, pdf files, images and any other type of files. Each downloadable product may have an unlimited number of files associated with it.
A service product is designed to sell any other, non - In-portal product or service that is not physically kept in stock and does not have to be shipped. An example would be an online babysitting business – when the customers pay for babysitting services online, yet there is nothing to be shipped.