You need stamps because if you don't have a stamp, they wont send it. First class is faster than second class, and so on.
That will depend on the value of the stamps you have. If you have one cent stamps you will need 190 of them. If you have ten cent stamps you only need 19.
what the price to mail letter to
you need ten stamps actually i don't know
3 stamps!
4 stamps
it depends on the stamp then you will know how many stamps you will need
maybe 2 0r 3 stamps
Stamps show that you have paid the money to have the letter delivered.
3 stamps.
I suppose you need one or two stamps to send the president. But my guess is just one.
If they say 42 cents on them, you need the additional 2 cent stamps to make up the difference. If they are 'Forever' stamps, they are valid for one ounce of First Class Postage regardless of the cost.
2