Even the most complex scientific theories can be explained to someone without a scientific background if the listener has a frame of reference for what is being said. You don't have to be a rocket scientist to understand the physics involved in going to the moon. It just needs to be presented in an inviting, familiar way using words that are part of the listener's vocabulary. By following a few simple rules you can describe almost anything and keep your audience members interested and entertained as they learn.
Review the current level of understanding of the people in your audience and adjust your vocabulary accordingly. Children have a more basic vocabulary than adults. Although some simplicity is effective for any audience, it's best to relate to the audience's level of sophistication and knowledge of the world to gain and keep everyone's attention.
Review any words that are not part of ordinary speech so people can follow along. If you are explaining a solar eclipse, you should first define the words "solar" and "eclipse." Provide a glossary if the subject is very detailed and uses many scientific terms.
Use visual aids, such as photos, illustrations and three-dimensional models to reinforce your explanation. It's easier to understand a solar eclipse, for example, if you use round objects and a flashlight to demonstrate the orbits of the earth and moon and how the moon casts a shadow on the earth.
Set the context of your presentation by outlining what you are going to talk about. This will help the listeners anticipate what will follow. Give a time frame for the discussion: Will you be reviewing past theories within a historical context or sticking to current thought on the subject?
Condense the explanation into a few concrete concepts the audience can take away from the discussion. This does not need to be a recap of your introduction, but should summarize the key points of your presentation.