I would like to give the users the possibility to download extra levels, whould this be possible?
Basicly let them add a new Sene and the play it.
is this at all possible? or do i have to define the lever as data and create a level generator?
If possible what functions should i look at?
If you own unity pro then yes, you can build a special form of player thats comparable to an asset bundle and can be loaded through the asset bundle mechanisms but can bundle additional scenes.
Otherwise, no, not if you don’t own Pro
Oki i do now own pro, i am just playing around, but i plan to buy it, will this worke on iphone? Do it have a name? what shell i google? 
Thanks again!
Its BuildPipeline.BuildPlayer with BuildOptions.BuildAdditionalStreamedScenes
Not fully sure if this is possible for iOS Projects though, would have to test. Asset Bundles work for sure.
And googling it won’t help you much I guess, cause you won’t find much about such stuff outside here normally