Where an action happens: で
Use で to set the scene for an activity.
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Put で after the place where an action happens. 図書館 で 本 を 読みます means “I read books at the library.” Think of で as marking the setting for the activity.
Use this pattern for activities such as eating, reading, shopping, studying, or waiting. To say where a person or thing exists with います or あります, use に instead. English “in” or “at” does not tell you which Japanese particle to choose.
Examples
けんさん は 図書館 で 本 を 読みます。
Ken reads books at the library.
レストラン で 魚 を 食べます。
I eat fish at a restaurant.
家 で 映画 を 見ます。
I watch a movie at home.
どこ で 買います か。
Where do you buy it?