An organism is either multicellular or it is not. An organism cannot have some parts of it being multicellular and other parts of it not multicellular.

Multicellular organisms include all animals, all plants, most fungi (not yeasts), many types of algae, a n Unicellular organisms include most bacteria, many protists, and some yeasts. As far as I know, all archaea are also unicellular, but there may be exceptions that I do not know about.

We are multicellular. Every organism you can see is multicellular. Many organisms you can't see are multicellular. The only organisms that aren't multicellular are the ones that have only 1 cell.