To use the hose attachment, first lift the black plug (above the nozzle side of the vacuum). Next remove the belt from the motor shaft using the belt lifter. Hook the belt on the left side of the shaft and rotate clockwise. Pull the belt gently towards you. See picture 6 (and Part A) of the manual; I've provided the link below. The belt lifter was included if your vacuum came with the attachments. If you need one, that is part 1880262000.
Once the belt is removed, depress the spring clip on the end of the hose. Align the spring clip with groove at the bottom of the opening. Line up the hose and push it into the cavity where the belt was. Pull gently to ensure that the hose is secured to the vacuum.
The manual for the Dirt Devil M08100RED is available on the product site: http://dirtdevil.com/products/details/m08100red/classic-hand-vac/
. The direct link is http://dirtdevil.com/file/1239/
. You can purchase accessories and parts from the manufacturer. Scroll down on the product page and click on the Parts link.
I hope this helps.