In other words, your horse will voluntarily submit to your direction. Round pen work should involve the least possible stress and danger for you and your horse. The process will also build confidence in both you and your horse, and it will teach you to speak the only language your horse completely understands - body language. I would like to highlight a few key points. Set small goals, and ask the horse repeatedly rather than forcefully to respond to you.
Persistence is worth more than force.
Keep the pace slow. A walk or trot is sufficient. You are not going to punish the horse by running it out of air or energy. Horses learn more quickly when they are not stressed. Watch your horse's sweat and breathing patterns.