Show and tell is a common expression about showing an audience something and telling them about.
It is a common classroom activity at early elementary school that is held by the English department.
It is used to teach young children the skills of public speaking. For example, a child will bring an item from home and will explain to the class why they chose that particular item, where they got it, and other relevant information. Some children choose to talk about themselves or any past experience they had for example; a trip, having a pet…etc.