Remove the cap from the Drain pipe by twisting (most likely counter clockwise). and attach the sewer hose by twisting the channels around the protruding plastic pins on the pipe.
Slide the other end of the pipe into the sewage connection in the ground or into your portable tank (this connection does not lock in but rather slips).
Some may have the locking channels on both ends for different types of connections, some amount of analyzing may need to be done to make sure that you have the proper fittings for your particular situation.
Try to make sure that the hose drops elevation from your RV to your destination (becomes lower).
It is also a good Idea to support your hose so that it has good downhill flow. There are products sold for this but I have found that a board works just fine, and it was free.
Pull your sewage valve open and let it drain for a few minutes. I usually let mine go until I can't hear water flowing through it.
Close the valve. If you are connected to a sanitary sewer line (!!! NOT A STORM SEWER !!!) then proceed to the next step but if you are using a tank like I am then I have added some extra steps at the end of this intractable for how I dump the portable tank.