Parts editor is difficult to understand

Hey,

How do you edit parts?

I have loaded a part with Parts (new) editor (which btw you shouldn't need to select a part to do that... really unintuitive design there)

All I want to do is add a golden square to one end, make it look like an SMA connector, so that I can make it look like the Venus GPS module. (which amazingly no-one seems to have made yet)

I am simply blown away. Why is such a simple task so insanely difficult.

Any suggestions are most welcome.