Worldwide the most common method of prepaying postage is by buying an adhesive postage stamp to be applied to the envelope before mailing; a much less common method is to use a postage-prepaid envelope
The postage required for postcards is generally less than postage required for standard letters; however, certain technicalities such as their being oversized or having cut-outs may result in payment of the first-class rate being required.
There ain't any news in being good. You might write the doings of all the convents of the world on the back of a postage stamp, and have room to spare. Finley Peter Dunne