Concepts can be concrete or abstract and are defined as sets of objects or events grouped together based on shared characteristics. There are different levels of understanding concepts from classificatory, where examples and non-examples can be recognized, to formal, where reasons can be provided. Instructional strategies for teaching concepts include presenting examples and non-examples, highlighting terms, using visuals or stories, and describing attributes. Learners should distinguish examples from non-examples, generate their own examples, and apply the concept.