hot water heater

Welcome!  Yes, unfortunately the manual is basically useless.  The best thing you can do is camp in Camp Driveway one night and start making a list of all questions and things that you discover you need.  The antifreeze intake line will be near the water pump, so one way to find it is to put some water in the fresh water tank (look for the big white cap about waist-height on the outside, your hose will just lay inside the opening), turn on the water pump (red switch inside), and open a faucet to start the pump.

To flush the lines of antifreeze you want to keep the water heater out of the circuit, so the valves should be opposite of what you describe.  The ones on the hot/cold lines should be perpendicular (closed) to the lines, and the one on the line between them should be parallel (open).  Hook your hose up to the city water connection (your hose will thread into this connection), and open every faucet including the toilet flush mechanism until it runs clear.  Once you are done, switch every valve behind the water heater to allow water into the water heater.  Then open the hot water faucet on the sink until it stops spitting air, which lets you know the water heater is full.  Do NOT start the water heater until you do that or you will damage the water heater.

You can leave the water heater filled over the summer.  If you feel you must drain it you can just open the low-point drain valves (located underneath the 'pod) and then open the pressure relief valve on the water heater (near the top, pull the short handle) to break the vacuum.  It will take a while to fully drain.  You can remove the hex head to drain it, but if you do put it back in to prevent rust on the threads - don't leave it out over the winter.  The anode is located behind that as you asked.