To be means to exist, to have life or reality. When you say “I am,” you're stating the most basic fact about yourself: that you exist in the world. The tree outside your window is. Your thoughts and feelings are. Everything that exists can be described with this small but powerful word.

Be is also the word we use to describe what something is like or what state it's in. When you say “The sky is blue” or “I am tired,” you're using be to connect a subject with a description. It tells us about qualities, conditions, and identities: “She is curious,” “They are ready,” “It is cold.”

The word changes form depending on who you're talking about and when: I am, you are, he is, we are, they are; I was, you were, he was, we were, they were; I will be, you will be, he will be. These are all versions of the same word, and English speakers use them constantly without thinking about it.

Sometimes be appears in commands or advice: “Be brave,” “Be yourself,” “Be careful.” Here it's telling someone to take on a quality or state.