I usually recommend to those who want to learn to treadle to start without any thread in the machine. Initially you don't even need to use fabric if you raise the presser foot up. I use both feet to treadle, one foot completely on the treadle plate and just the "toes" of the other foot on the front edge of the treadle plate. Now, pull the handwheel towards you (if you're using a Singer). You will feel the treadle plate move----go with that movement. I think it's best to go a bit faster now than you would if your were actually sewing; this helps you to become "acquainted" with the motion.
Next step: place some fabric under the lowered presser foot, but still without any thread. Practice "fake sewing" like this with the fabric being fed by the feed dogs. Learn to stop the machine (stop treadling) without having the handwheel turn suddenly in the opposite (wrong) direction as this motion will break your thread. Until you become skilled at stopping with your feet, you will need to reach over and stop the handwheel when you stop the foot motion sort of simultaneously.
Caution treadling may become addictive; some people have been known to seriously neglect their expensive computerized machine once they learn how rewarding it is. Enjoy!