Summarize:

Put your hand in your pocket and use your hand to press your erection against your leg. Continue to hold your erection through your pocket so that it isn't visible on the outside of your pants. Put your hand in your pocket, lift up your erection, and put it in between your waistband and your waist. This will hide your erection when you're standing or walking. You'll need a belt or an elastic waistband to do this. When you're sitting, it's easier to hide your erection. Cross your legs and pin down your erection with your thighs. This may be uncomfortable at first, but your erection should eventually disappear.
Pin down your erection with your hand in your pocket. Put your erection in your waistband. Cross your legs.