がいる

「がいる」 is used to:
1. Announce the existence or presence of a living person, creature, or moving object that behaves like a person or living creature.
When you want to indicate that a living person, creature, or moving object that behaves like a person or living creature exists or is present in a specific location, you add the noun indicating that location with the particle "に". Example: 教室に七海先生がいます。 (In the classroom, there is Teacher Nanami.)
2. Indicate the subject owning a particular living person, creature, or moving object that behaves like a person or living creature. Example: 兄が一人います。 (I have one older brother.)