First, clean off the drain plug. It has a magnet to catch any metal in the oil and some flakes are normal. Once the plug is clean, put it and the new washer back in the differential and use the torque wrench to tighten the drain plug to 44 Nm or 32.5 ft-lbs.
Now take the flexible tube and feed one end into the tube for the dip-stick. Put the funnel on the other end of the flexible tube and start pouring in the new fluid. Take your time on this step and check the fluid level often (with the dip-stick). If you put in too much fluid, you can drain some out from the bottom. I used over a quart (the spec. is 1.2 - 1.4 qt.) to get the fluid up to the "F".