How to define/delimit/outline a drainage basin. (step 6)
The sixth step is drawing the divide. Now you "simply" connect the dots. Follow the contours and stay along the ridges. The line should have the tributaries from the basin you are defining on one side and all other tributaries on the other side (your divide should not cross any of the tributaries). See the red line below.
Now, draw the drainage divide the rest of the way around the drainage basin by following steps 1-6.
You can now determine the properties of the drainage basin including its area, the total length of the stream channels you drew, the total relief (highest point-lowest point), the drainage density (total stream length/area), and the relief ratio (total relief/area).