If you use concept art to help you envision what you want to model, specially in case of terrains, houses and more mechanical parts, how do you draw it, using which software? Or do you draw it on paper instead?
I know that pretty much any drawing software from MS paint to basic drawing apps on a phone work, but which one is the most user friendly with most options for this kind of thing?
you can draw in 2D in Blender
but blender is 3D so you can draw objects in 3D to represent anything like furniture house - building ect,
you can even add trees grass ect,
I mean if your ready to invest time to learn blender then you can do almost anything you want in 3D or 2D!
but blender is not an image editor!
happy bl
I don’t have much experience with this, but from what I’ve heard Krita is great for this kind of work:
https://krita.org/en/
Since “I can’t draw” … 
… I often go immediately to "actually model something." First, I decide on the scale that I will use, and lay out a set that is “actually that big.” Then, I start creating geometric shapes that are also “the right size,” and I give each one a Name. Then, with “Name” rendering turned on, I start doing OpenGL Preview renders, which can be completed in nearly real-time and which are accurate with regard to cameras, etc. And I basically start figuring things out by moving little cylinders, cones, cubes and spheres about.
Significantly, these sometimes become(!) the actual sets, the actual props, the actual cameras, and eventually, the actual shots.
“To scale” is actually very important because Blender does model a physical 3D world with cameras in it. Your powers of imagination can tell you that the box labeled “Lamborghini” really is one when it’s still nothing more than box, but if it’s the wrong size relative to everything else in the shot, you’re sooner or later going to find yourself stuck in a corner.