I've not talk about this since before I Joined Serebii.. Mind you for my copy back then wasn't official. You won't need to know C++ for the more "tradtional" RPGs with RM2k3.
RPG Maker 2003 being out for more than 12 years now, it's had an unoffical fan translation out for almost all that time.. It's goes under RPG TSUKURU 2003 in some sites to distance itself from the offical version on steam. Oh, while I can remember it, some tips and tricks for RPG Maker 2000 works for RPG Maker 2003 due to lots of things being carried over.
This page should help:
http://rpgmaker.net/tutorials/rt2k3/ and
http://www.blade2k.net/writing.php?type=0
The screen you see Normally is the "Map" screen. There are 3 modes, which I'll call "Terrain" "Clutter" and "Event", these may be different names, but the effects are the same.
Terrain Mode will allow you to draw the landscape. Some tiles will limit your Characters Movement. Just be aware if you place tile thinking it's for a floor then realise it's intended for a wall.
Clutter allows you to drop some Clutter that doesn't have an event tied to it. These will not move The Towns and Castles in the "overworld" map are generally this. You can hide events on Clutter object.
Event mode, will let you See and place events. You can give a event an Character Sprite, and can move. Events range from Dailogue, Shops and Trigger for Story battles. Events will trigger if you character steps on it or talks to it, depending on which one you choose.
There is a huge amount of stuff hidden in the Database option, which allows you to create characters, certain terms, weapon, Mobs and Mob Groups quite a few other things.
Personally I'd start with looking at someone else game first. I don't know if there was a test given.
This site is very lax on the "copyright" front but its' just about the best place to find or create Rm2k3 stuff.
http://charas-project.net
You may need to look at this page if you want to understand why something won't work:
http://steamcommunity.com/app/362870/guides/#scrollTop=47
(I used to post these in every post on the forum I used to be on.)