でMeans, tool, and language marker
で marks what someone uses to perform an action. It can identify a tool, vehicle, language, or other practical method.
What the marked noun tells you
The phrase ending in で answers a question such as “with what?”, “by what means?”, or “in what language?” The following verb names the action performed using that means.
Core uses
Notice how each marked noun is a natural means for the action that follows.
Means and location
The same particle can mark either where an action happens or what is used to perform it. In the example below, the first で phrase names the location, while the second names the language used.
教室で日本語で話します。
We speak Japanese in the classroom.
Analyze教室で answers “where?”, while 日本語で answers “in what language?”
Tool and material
A tool is used to perform an action; a material becomes part of the thing being made. Both can be marked by で, so identify the role from the noun and verb.
木で箱を作り、金づちで釘を打ちます。
I make a box from wood and drive in the nails with a hammer.
Analyze木で names the material, while 金づちで names the tool.