I am trying to get accustomed to Krita, and I have a really simple question:

I would like to select the black square below. It's often very difficult to select a shape with a computer mouse at exactly at the right pixel. How can I drag the sides of selection to the right place once I zoomed in? i.e..: in the example below I would like to make sure the I have selected all of the black pixels. (For example in paint.net there is a separate arrow selection tool to drag the sides of the selection manually. I am sure it is here somewhere too, I just cannot seem to find it.)

ps.: I do not want to do a selection based on colour, because that' not always possible, and this is just a rudimentary example.

In this case there would be two ways. Either press the Alt key while dragging the rectangle to move the rectangle while you are dragging it with the rectangle selection tool. The other way would be to use a vector selection (can be turn on in the tool options).