Symphony.

ok, i am confused. All I can tell from looking at Symphony's database is that a lot of joining is going on. And that no one seems to write comments in his/her code.

I want to write an extension and I want to have my own field-types. I guess I could just have my own table and not care about symphony stuff but that would be so uncool. That's why I would like to create field-types.

So how do I create my own field-type "email" for example? How do I get the backend to let me create Fields in Sections with the type "email" instead of textarea?

Have a look at one of the existing extensions. I have been playing around with these to understand the system. I found Rowan's extensions quite helpful as they are well structured and have at least a few comments in the code. And there should be some information in the old 1.7 wiki that is still usable.