で

で after a place says the action happens there – "at" or "in". The place usually comes before the thing acted on, and the verb stays last.

で or に

で marks where something is done. に marks where something is, with あります and います, and where something goes, with verbs like いきます行きます.

• × 図書館に勉強します → 図書館で勉強します
• × 図書館でいます → 図書館にいます

When あります means an event takes place, the place takes で, because an event is something that happens.

By, with, in – the means

After a vehicle, a tool or a language, で says what the action is done with.

"On foot" is the exception. In everyday speech it is あるいて歩いて ("walking"), not a noun with で. The noun とほ徒歩 does take で, but it belongs to signs and writing.

• × 足で行きます → 歩いて行きます

Usage notes

These go beyond the place and the means.

Made of, made from

After a material, で says what a thing is made of.

Because of

After a noun such as an illness, the weather or an accident, で gives the cause of what follows.

Among, and in total

で sets the range a statement holds for, which is how "the most … in …" is said.

After a number or amount it gives the total, or how many people do something together.

The で that is not this particle

The で that joins a noun or な-adjective to what follows is a form of です, meaning "and". It has nothing to do with place or means.