As long as your letter is under an ounce it is just one stamp no matter which US state you are mailing a letter to.
4 stamps
what the price to mail letter to
it depends where you send it to
The same it takes to send it anywere else...
only one
This depends on where (which country) you are sending your mail from.
You need 1 stamp to mail a letter/package throughout Canada
One Ounce=One Stamp.
From the US, 94 cents for a letter , one ounce of less.
Stamps depend on weight, not distance. You can find much more here: http://www.usps.com
If this is just a post card you will only need the one stamp to mail it within the US.
That is what the US issues stamps for, so that you can send mail to anyplace in the world.