Most of us gesture when we speak one on one. However, many of us have no idea about what to do with our hands when we are in front of an audience. The answer is that we do the same thing in front of an audience that we do when we speak one on one. I've heard reports that some high school speech teachers tell their students not to use gestures. This is bad advice.
Gestures are an important to effective communication.
The problem is that when we get nervous our hands may shake and we want to hide them. Or, we may fiddle with a pen, scratch our nose, or find another way for our hands to distract the audience from our message. If you can't figure out what to do with your hands or they misbehave on their own, you may want to rest them on a lectern or put them behind you. It's best to let them help you communicate the way you normally do. Use the dialect of commerce.