Hi I'm sorry if I don't come out to clear on what I'd like help with, but I'll try the best I can since english isn't my frist language. But.
I'm used to Sai which has a selection toll/brush. Working more or less like photoshops masking layer. You paint what you want to select. I usually use this to fill large spaces and/or use later for staying inside that area and not draw outside lines or that area. Like locking layers and group layers in Sai.

So far in krita I've just painted those part and chosen a local selection layer to that layer. But I'm wondering if that is the most efficient way to do this? Instead of having many layers for each section which afterwards needs to be flattened to be able to blend layers together. It would be nice if I could work like in photoshop by saving selections in mask and just choose that preset for it and in process be able to easily blend between different sections since it's in the same layer making it look more smooth.
But so far when I've tried to use maskin I'm ready to toss the table. I see what I'm drawing after releasing the button which is highly frustrating since I can't really see where I'm drawing nor is it easy to edit.
Is something wrong? Is there an easier way to do this? Some setting that needs to be toogled? What? Plz help.