For the love of Gosling, stay away from GUI builders. They hide what’s going on under the hood, which can be great at first, but then you’re screwed as soon as you need to add any amount of customization. They also create unreadable code, so you’re double-screwed if you have to go in and manually change something.
Write your GUI code by hand until you understand what’s going on. Then if you still want to use a gui builder, at least you’ll know what you’re getting yourself into. But chances are by then you won’t want to use one anyway.
That’s just my two cents, but I’ve seen enough people backed into a corner by starting out with a gui builder instead of actually learning how to code.