When we talk about two things, we can "compare" them. We can see if they are the same or different. Perhaps they are the same in some ways and different in other ways. We can use comparative adjectives to describe the differences.
We can use comparative adjectives when talking about two things (not three or more things).
In the example below, "bigger" is the comparative form of the adjective "big":
In this lesson we will look first at how we make comparative adjectives, and then at how we use them: