What it means
てある describes a state that exists as the result of someone performing an action. It is commonly used with a transitive verb in the て-form, and it often suggests that the action was done intentionally for a purpose or preparation. The thing in the resulting state is usually marked with が. The polite counterpart is てあります.
Usage note
てある focuses on the resulting state and the action that caused it, while ている usually describes an ongoing state or a state without emphasizing intentional preparation. Use a transitive verb with てある, not an intransitive verb.
How to use it
ポスターが壁に貼ってあります。
A poster has been put up on the wall.
ポスターが壁に貼ってある。
A poster has been put up on the wall.
Example sentences
会議の資料が机の上に置いてあります。
The meeting materials have been placed on the desk.
旅行のために、かばんに地図が入れてあります。
A map has been put in the bag for the trip.
玄関の電気がつけてあります。
The entrance light has been turned on.
授業で使う本が教室