4x6 envelopes are considered business type mail and therefore do fall under the acceptable size for a regular stamp. Beware that some post offices do have different regulations.
NO, they have to be an already stamped envelope from the post office
A 1099 form, mailed in the required envelope, should be stamped with a regular first class, one ounce, stamp. As of 2014, a first-class stamp is $.49.
Many envelopes will have a box in the top right corner which says something about the postage. If does not have that, you usually place the stamp in the top right corner of the envelope. If you have issues, then you should go to your Post Office.
Its called a stamp square or stamp window.
Just one stamp if it's a regular letter. A forever stamp will get the job done but if it weighs more than the a regular letter, you may want to stop by the post office and get it weighed first
To cancel the stamp so that it can't be used again.
Not necessarily. Many stamps are valued for their cancellations and sometimes the envelopes they are "tied" to.
47 cents, or one Forever stamp for the first ounce.
The Post Office. Stamp Collectors. Stamp Dealers.
As of this writing (June 2009) it is 44 cents. Check with the post office web site for current cost.
From a Poat Office From a Poat Office
The stamp has to be accepted where you mail the letter. If you are mailing in Canada, you need a Canadian stamp. If you are in the US mailing to Canada, you can use a US stamp.