I won’t keep you in suspense: The two most basic verbs are “be” and “do” and all their forms. In principle, you can substitute any verb with the appropriate form of “be” or “do.”
I remember in high school English that our teacher suggested that you could always tell if a word was a verb by asking yourself if you you could go to the front of the room and “do” it. Naturally, some things would be preposterous, but if it worked as a sentence, the word was a verb. So, fish, for example. I could go up to the front of the room and fish. That was not actually possible, but the sentence worked, so “fish” was a verb. (“Fish” can also be a noun, but that’s another topic.)
This also works with “be” in a way. Take “smell.” You can go to the front of the room and smell. Picture yourself sniffing the air. It’s something you can do, so it’s a verb. But what if you go to the front of the room and everyone recoils at your aroma, because you smell? (I just remembered that Samuel Johnson pointed out to the lady sitting next to him that the correct verb was “stink,” so let’s switch to that.) So can you go to the front of the room and stink? Yes, but it’s something you are. This is easier to see if we add an adjective, and to be colloquial, let’s go back to smell. You can go to the front of the room and smell funny. Now substitute “do” for “smell. It doesn’t work. But substitute “be” and it works: You can go to the front of the room and be funny. Or not so funny. Hamlet was substituting “be” for another verb in his famous soliloquy.
Verbs that “be” can replace are called linking verbs. (We call all other verbs action verbs.) In linguistics, the term is copulative, because they couple things together. Linking verbs are equivalent to an equals sign. In many languages you can even leave linking verbs out, including in English. (Hnngh. Hairface hungry.)
A word of advice: In your writing, if you can, don’t use “do” or “be.” Every other verb in the language has more color, more specificity, more oompf, than those two tired out, vague, non-committal, unspecific verbs.
Next time I’ll tell you another thing about do and be, but it’s a little complicated, and this post is long enough.