Well, i got a model but i want it to looks like if it where in front a mirror. Something like this:
Mirror modifier
The object is mirrored about its origin or add an empty to use that as the mirror axis
Sorry, my english is bad, can you explain it a little more detailed?
Go to link and read the wiki.
Add the mirror modifier, properties panel under spanner icon
Mirror modifier tutorial http://blenderdiplom.com/index.php/tutorials/item/91-ressource-blender-modifiers-explained
The settings are pretty clear
This is not what im looking for, the video teachs how to MAKE a model with the “Mirror Modifier”, but i just want to flip horizontally my model from this: 
to this: 
not making a new one or making a symmetric model a just want to flip it horizontally.
As Richard said, you can do that with the mirror modifier. Or you can duplicate the object (shift+d) then scale -1 on the x axis (sx-1)
Or Object / Mirror menu entry (Ctrl+M)
Thanks a lot!
Thanks thats what i was exaly looking for ^^!