The thing that is under the water bucket is the alpha tool or somthing i belive that only draws on drawn lines it helps to do some details and shading the under the alpha tool is the uhm is like somthing to use on the wall (i have lost my memory;-;) it also good for shading, for better one click on the certain color and go under color bar it will show you the capacity bar (suggesting to use near 0.1-0.3) and there will be also layers that can be found next to small trash can (not that trash can in the up corner) + = add a layer, - = delete a layer. And that's all I belive

Believe* any other buttons is almost easy to know or learn about so yeah-