So it's similar to Netflix, with one monthly price for all-you-can-watch streaming, one for disc rental by mail and a price for both services combined. The differences from Netflix being that there are also rental streaming titles and a game discs by mail option.
Here Amazon does not rent discs. The all-you-can-watch streaming, called Amazon Prime Instant Video, is an adjunct feature of the Amazon Prime program, which has an $80/year price and includes some free-to-borrow novels for Kindles (no more than one per month). Its original and principal feature is no-additional-charge 2-day shipping; all the rest (IMO) is just inducement for you to join and get that shipping, which will probably increase the amount that you spend buying merchandise from Amazon (many apparently lower e-tail prices turn out to be not lower than Amazon when you add 5-8 business day shipping). Amazon also has rental video titles which are not free for Prime members.