N5
がある
To be, There is
部屋に椅子がある。
There is a chair in the room.
Explanation
「がある」 says that a thing exists somewhere, or that someone has something: 「机の上に本がある」, 「時間がある」. It is used for objects (a desk, a book, a car), natural features (a mountain, a river), plants (flowers, trees), abstract things (time, money, a promise, a problem) and events (an exam, a party, a meeting). The negative is 「ない」 (polite 「ありません」).
Mixed up with
People and animals (things that move on their own) take 「いる」; objects, plants and abstract things take 「ある」: 「犬がいる」, 「木がある」.
There is no 「あらない」; the negative is only 「ない」.
For an event that takes place, use 「ある」 but mark the place with 「で」: 「教室で試験がある」.