The first ossicle-hammer-is attached to the back of the tympanic membrane.
When the tympanic membrane vibrates, so does the hammer.
In turn, the hammer sends the vibrations to the attached anvil, which further sends the vibrations to the attached stirrup.
The stirrup makes the connection with the end membrane, the oval window.
The three ossicles act like levers that greatly amplify the vibrations, which, in turn, cause the attached oval window to vibrate.