Before you start, think long and hard if your problem hasn't already been solved. I'd be doubtful if I can create a text editor on par with even the average. If you thought about it, long and hard and realized that you really do want to write one, I'd start by downloading the source to one of the open ones (pick one: http://en.wikipedia.org/wiki/List_of_text_editors#Free_softw..., but avoid emacs it will be too complex for you) and study how they solved the usual text editor problems, and where it went wrong. This should also be able to teach you about the common way to construct the architecture of a text editor.

Pick a set of features you want to start with and how you will interact with it. Pick what language/API/platform/etc you want it to work under and start reading docs and thinking how to go about writing your own.

Not to discourage you, but you probably won't be able to match most editors having never written one before. If you just want a hobby project, it be useful to start it for the experience. It might teach you a lot about software, or however, it might just frustrate you.

edit: What is your experience in? What kind of code do you write now?