button
The German word for button is 'Knopf'. It is a noun that is used to refer to a small, flat piece of material, usually round or square, that is attached to a surface and can be pressed to operate a machine or device. The word can also be used to refer to a decorative button on a piece of clothing.
The button on your shirt is loose.
This sentence is a common useful phrase which could be used to tell someone that a button on their shirt is not tightly secured.
Please give me the red button over there.
Here, the speaker sees a red button somewhere and is asking the listener to pass it to them. This could be used in a variety of contexts like sewing, machinery, etc.
Do not press the yellow button.
This phrase could be used when warning someone not to press a certain yellow button, maybe because it could have some harmful effects like machinery operation situations.