Just one of the correct denomination for the fee or any combination of stamps of smaller value to make up the fee.
1
Lots.
1 stamp is required.
sometimes 2 if its big if letter then one
Ask at a post office in Oregon.
how many forever stamps = .94
I successfully mail CDs all the time with 2 stamps.
4 stamps
how many first class stamps does it take to mail a 4 oz letter and package
That many
If this is just a post card you will only need the one stamp to mail it within the US.
5