What is the recipes of chocolate cake? And what is the best method for decorating chocolate cake?

There really isn't one best chocolate cake recipe, there are lots that work great.  You can search in the recipes in Cake Central and see some that people use.  Or a general search on google.  There are also lots of ways to decorate a cake, the flavor doesn't matter.  Simple as just using an icing on it or you can decorate it.  You can look in the galleries to get decorating ideas.