Amazon prime is free (pre-paid whichever way you want to look at it) 2-day shipping on all applicable items. Usually, these items are from Amazon themselves and are either cheaper in general or cheaper when the shipping cost is accounted for.
Also, you get video streaming. Prime is $79/ year but if you're a student it's only $39/year. You can share prime with other people (split cost) but they have to use your account. This means that they can see your information and if you have a credit card saved to Amazon then they can order stuff with your card. If you want to share, I suggest doing it with a close relative and/or friend.
I might sound like an Amazon rep but I'm really not. However, Amazon is probably the best invention second to the Raptor