Also check Youtube - loads of videos on Doepfer modules.  Rauls World Of Synths  Raul's World of Synths

 

 is a huge resource.  I sometimes find his videos a little slow and dry, but that is my taste, not his ability. He has put an awful lot of effort into his videos, and has covered many of the Doepfer modules in great depth - a great set of tutorials.  Also just search YT for Doepfer and the module you are interested in, for many more examples.