Right now I can't draw at all. I can't even rotate a cube in perspective. Is it normal to not be able to vividly imagine things in your head? I can only do what you call symbol drawing and even that badly. I could maybe draw a recognizable symbol of a cat but something like a sloth would require me to look at an image of it while drawing. I can't even draw a proper straight line or circle. My lines come out wavy and my circles oval and with the lines not connecting.

When I try to draw something from life I can only draw the outlines with very simple shading. The proportions all come out wrong and I have no idea how to draw any textures.

But I have a pretty specific goal. I want to focus on drawing people only. I don't want to draw buildings, landscapes, cars, dragons... I don't want to draw comics or animation or dramatic or moody pictures. Also I want to draw from imagination. I don't know how doable that is without using any references at all but I don't want to just copy what I see like a camera. Of course I understand that I might have to do that in order to learn.

So with all this in mind how do I go about it? Where do I start? What skills do I need before I progress to the next step? I know that there are books on figure drawing and anatomy but aren't these for people with decent drawing skills? Do I need to get decent at drawing from life first before I start working on drawing from imagination? I know that it takes a very long time to learn drawing so I don't want to waste time learning something I would not need.