Below are inline answer for your question.
1) whar r coupons
Its unique one time usable code which you can apply to get Free credit.
2 are they genuine
Yes.! 100% genuine.
3 from where to buy
No need to buy any coupon, If you are first time using their advertising feature they will provide that to you for FREE.
4 by using if facebook blocked us
No, They won't block you as long as you follow their rules.
5 they r not cheaters
Again, If you buy coupon from someone there is high chance of terminating your account. So don't trust on anybody.
Hopefully I've cleared your doubts.