Beginner needs some help getting started

Hi all my name is Xandor and I just began trying out the dev kit.
Must say its quite frustrating as nothing appears to be working (not a real suprise, cause i know squat), ive been watching tutorials of how to start on youtube and read the website where u can download the epic games launcher.

Now, I actually managed to create a field to paint and whatever, but when I save it and reopen it all the paint is gone. the whole map is black and i cant repaint it, it just stays black. What did I do wrong?

I will have millions of questions though, hope thats ok.