Magazine subscriptions are a commitment to purchase magazines as they are published for a specific period of time. Most magazine subscriptions are for one year's worth of magazines. Getting a magazine subscription usually gives you a considerable discount from buying them in bookstores, often upwards of 50% off of the list price.
Often times companies will give an incentive to sign up for a magazine subscription such as your first few issues free, or a free gift for signing up.
Recently magazine subscriptions have been on the downfall with the popularization of the internet. As a result, most magazines offer an online magazine subscription as well. An online magazine subscription will give you yearly access to a website that contains all the same information in the paper version of the magazine, and often more.