To exist or be present (usually used for inanimate objects or things). Commonly written in kana.
机の上に本がある。
There is a book on the desk.
この町には古い神社がある。
There is an old shrine in this town.
部屋に誰もいない。テレビだけがある。
No one is in the room. Only the TV is there.
To have or possess (used as 'to have something' or 'there is something possessing a property').
財布に現金がある。
There is cash in the wallet.
このパソコンには十分なメモリがある。
This computer has enough memory.
To be located; to indicate the position or whereabouts of something (e.g., a building or place).
駅はこの通りをまっすぐ行ったところにある。
The station is straight ahead on this street.
店は駅のそばにあるから便利だ。
The shop is near the station, so it's convenient.
To be equipped with or to possess certain features (used with 'to have' equipment or facilities).
この車にはエアバッグがある。
This car has airbags.
この部屋にはエアコンがないが、扇風機はある。
This room doesn't have air conditioning, but it does have a fan.
To happen or occur; used to indicate that an event has taken place (often in expressions like 'there was/wasn't ...').
昨夜、近くで事故があった。
There was an accident nearby last night.
会議で問題が起きたらすぐ連絡してください。問題があった時の連絡先は同じです。
If a problem arises in the meeting, please contact us right away. The contact for when there's an issue is the same.
Auxiliary use after the -te form of a transitive verb (〜てある) indicating that an action has been done and the resulting state remains (someone did it and left it in that state).
窓が開けてあるから、部屋は涼しい。
The window has been opened (and left open), so the room is cool.
本はテーブルの上に置いてある。
The book has been placed on the table (and remains there).
明日の準備は全部済ませてある。
I've finished preparing everything for tomorrow (and it's all ready).