Addition is the process of combining collections of objects into larger collections. It involves adding different numbers together, such as 3 + 2 = 5, 4 + 6 = 10. Examples are provided of adding sets of bubbles and solving addition equations like 5 + 5, 7 + 3, 4 + 4, and more. The document provides an introduction to the concept of addition through examples, sets to add, and equations to solve.