Visit your local craft store or purchase liquid chalk pens online (see References). The pens should be able to be easily removed with household cleaners and should not be confused with marker pens. If you are uncertain whether you are purchasing the correct type of pen, ask to make sure. Purchase a pen in a color which will be clearly visible against the chalkboard background. Plain white is a good choice.
Write on the chalkboard using the liquid chalk pens. Writing clearly on a chalkboard can take some practice due to the angle of the writing surface. Use large letters so the text or diagrams can be seen by the entire class. Consider purchasing a meter stick to help guide your writing on the board if necessary.
Remove the liquid chalk per the manufacturers instructions. Common products for removing this type of marker include non-ammonia-based cleaners or standard window cleaning sprays. If using window cleaning sprays, consider wiping the board again with a damp cloth to remove any cleaning product residue which may make it difficult to write on the surface immediately afterward.