I'm searching for the documentation of MeshLab, but from the Help-Menu of ML I'm forwarded to the download page of the beta version of the program, but I do not find the documentation there.
Could someone share me a link?
You cannot find the MeshLab's documentation cause...there is not MeshLab's documentation :)
Anyway here you will find a complete set of tutorials on how to use MeshLab in the basic scenarios https://www.youtube.com/user/MrPMeshLabTutorials
I hope you will find them useful.