This is a web-based instructional module on the algebra of sets.
http://www.math-only-math.com/laws-of-algebra-of-sets.html
Union of Sets:
https://www.basic-mathematics.com/union-of-sets.html
Intersection of Sets:
https://www.basic-mathematics.com/intersection-of-sets.html
Venn Diagrams for union and intersection:
https://www.mathsisfun.com/sets/venn-diagrams.html