i Have a musicfile that is to loud. How do i reduce the sound?
Effect → Volume and Compression → Amplify and enter an negative Amplification value. You’ll probably need more than -3dB reduction.
Note that if it’s clipped (distorted), lowering the volume will not eliminate then distortion.
BTW - Some player software supports ReplayGain and Apple has Sound Check which tries to automatically make all of your music approximately equal in loudness. Or if you have MP3s, there is MP3Gain which changes the actual file so it doesn’t depend on player support.
You don’t mention what computer or operating system you are using, but most are similar.
Look for a speaker icon 
and click it. It should bring up a sound volume control. Drag that control to the left.
One day a fellow was lost in a city and could not find his way. He spotted a police officer and asked the officer where he was. The policeman replied, “you are in a car.”
WDYM by “too loud”? You mean distorted?
And that joke was originally about two physicists vs a mathematician. It has a punchline too: “— You’re in a car (balloon, boat…). — This guy’s evidently a mathematician. — How’d you know that? — Because he gave me an answer that is as exact as it is useless”. 
I think I favour the fancier version of the joke.