You get everything sony listed, like 2 free minis, 1 psone game, 1 psn game and other goodies like dlc avatars and themes, and then discount on various things.
All of these things are stread out throughout the whole month. So yes, each week we get something new for ps+.
We get monthly content, subject to being made available throughout that month. No set schedules other than monthly content. Here's what we get each month:
One PSN Game
One PSOne Classic
Full game trial
Exclusive PlayStation Store discounts 20% to 50% off
premium game elements/add-ons
And periodically we will get advanced invites into selected betas and demos.
Straight from the official blog.
1 year subscription costs $49.99 (for a limited time you can get 3 months free with this one, so you get 15 months for the price of 12)
3 month subscription costs $17.99
More details at the link below