Forever
As of 2016, one standard forever stamp costs 49 cents.
It is a forever stamp. It is good for the current value of a first class stamp.
An unused Forever Stamp is worth whatever the current postage rate is. At the moment that's 49 cents.
Yes
A first-class stamp is not the same as a forever stamp. A forever stamp holds the value of a first-class stamp regardless of how often the rate for first-class postage has increased. A first-class stamp only holds its face value.
Yes, you can ... forever ...
Forever stamps will have the word FOREVER printed on them. If the do not have a value and do not say forever, they have a fixed value.
No, only one Forever stamp has been issued. It has a value of 44 cents currently. There is a listing of USPS postage stamps that have been issued without values on their website.
The Liberty Bell is pictured on the Forever Stamp. They are worth the current value of a first class stamp, which is 44 cents in 2009. They can only be used for US addresses.
No, it is not a Forever Stamp.
No you cannot use them. Forever stamps can only be used for domestic (inside the US) mail. They must have a value on them for international mail.