First prepare the tools, solder (DIA 0.8mm, FLUX 2.2%), a 30-W soldering iron, some DB-9 female connectors, a cutting plier.
The cable used here has 5 inner wires, red, black, green, white and drain. For one end, strip about 2.5-cm cable jacket with cutting plier.
Put heat-shrink tube (yellow in image) on the drain wire, leave about 2-mm conductor outside, heat the tube with soldering iron. Strip about 2-mm jacket for the rest 4 wires.
Find a comfortable way to hold the cable and the solder with one hand, hold the soldering iron with the other hand, feed a little bit solder onto wires' tips.
Fill DB9 female connector slots with solder, in position 2, 3, 5, 7 and 8.
Place a wire on top of its corresponding slot, touch (the touch should be within 2 seconds in case connector damage) the soldering iron onto the joint to melt the solder on the wire and the slot, join the wire and the slot together, remove the solder iron, keep the position a while to allow the joint cool down. The joint should be polished and secure. Repeat this steps for other wires.
Install the case.
The other end can be made by repeating the above steps.