Hi @anonymous_user_cee37bff, this may be a little obvious answer, but I had problems with this my first time working with landscapes in the UE4.
When you create a landscape, you have to toggle the Game View Mode (press G while in the editor!) to see it and to be able to work properly over it.
I mean, this in case that your landscape doesn’t even appear (if you don’t have a skysphere or similar, it may look as it is black!). But if your landscape is actually there, this obviously isn’t the answer…