No need to be embarrassed — we all start somewhere!

In that case, I think you're fine with Noteflight or MuseScore. If I were you, I'd play with both and choose whichever one you feel is more intuitive.

You might also give Soundslice a try (https://www.soundslice.com/) — it has a web-based music notation editor that has practice tools built in (like a visual piano keyboard to show you where to put your fingers).

It's free to use for your use-case. And though it's not open-source, it was developed by one of the people who created the Django web framework (me!) — so maybe my past open-source work counts for something.