Placing the person. because this 1 had to be behind the vessel, it easy to use the select option of that layer, makes deleting sometimes real easy. You just hold the cntl key en r/click your mouse on the preview of your layer.
Drawing lines, the best way is to use your pencil. Put 1 dot at the beginning, then hold the shift-key while placing the second dot at the end. The shift function will now place a line between punt 1 and 2. easy :)