Karen is cooking today. In this sentence the word cooking not only looks like a verb and sounds like a verb, but it is also acting like a verb.

Cooking is something that Karen loves to do. In this sentence the word cooking is not acting like a verb. It sounds like a verb and looks like a verb ,but it is acting like a noun. Let's see why. The word "is" is the verb, so what is the something that Karen loves to do: cooking right! Therefore, cooking is the subject of the verb "is".