Pandabear: You pay for it with the membership fee of $80 per year. If you make a bunch of purchases and always need expedited shipping then it maybe worth the money.
Amazon already gives free standard shipping on purchases over $35 on products that are shipped and sold by Amazon. So I don't see much use in spending extra for Amazon Prime.
Not on things that come from Amazon's warehouse. If it comes from another seller, than you still have to pay.
No, but you can take a trial and it will not charge you and you can take advantage of the free next day shipping for 30 days.
Not in addition to the cost of prime unless they want 1-day
nope. But the membership is $80 per year.