Scroll down to view stringing and unstringing demonstrations for both longbows and shortbows.
Make sure the bottom limb is high enough on your foot/shoe to keep it out of the dirt. Check your shoes for metal hooks and eyelets, and avoid placing the bottom limb on a metal eyelet while stringing. Metal shoe parts are notorious for denting/gouging the wood.
A right-handed archer steps through the bow with his/her right leg, and pushes the top limb with the right arm. A left-handed archer steps through with his/her left leg, and pushes the top limb with the left arm.
Stringing a Longbow:
Stringing a Shortbow: