The easiest way to create a "castbar"?

[Anuki]

Hi Developers.

I'm fairly new at programming addons.. I have completed my first addon last week, which was purely chatframe-based.
Now I've a new idea for an addon, which should show a kind of castbar for a few seconds, after an event is fired.

I really have no idea how frames, etc works in wow and the tutorials I've found couldn't give me the information I need and the code of, for example, quartz is not that beginner-friendly.

Is there a fairly simple way to create a kind of castbar quick and easy? Does anyone know a good tutorial (I don't like to use, for example, Ace, because I want to learn it for myself, how it works )?
A simple help, how to show a graphic for a few seconds ingame (best as a function) would be perfect and I would be happy if someone takes the time to help me here.

Best regards,
Anuki

P.S.: I hope my English is good enough to understand me