I did a lot of searching for Tutorials to learn how to install Ruby, Gems, Rails and all the needed stuff. In the end I ended up with a Mac OS X flooded with useless files, old versions of Ruby, old Versions of Gems, incompatibilities and much more. Webrick got up an running, but mysql didnt work, sqlite3 was missing and so on. So I decided to delete everything around Ruby and Rails and start from Scratch. This time I tried to find a tutorial that is about the newer Versions of ROR.
So, there is not much to say:
if you want to start your ROR career on your Mac,
follow this Tutorial -> http://pragmaticstudio.com/blog/2010/9/23/install-rails-ruby-mac