Welcome, and congrats on your new iPod.
Simply plug it in (you implied that the mains power adapter is an option, so I suggest using that) and let it charge until it finishes (battery icon stops scrolling, and the lightning bolt remains on the screen). There is absolutely no need to stress out over plugging it in for any exact amount of time, or even running down the battery between charges--feel free to charge it and use it as you please.
I can vouch for this out of personal experience: I keep my battery topped off most of the time (it's almost always plugged in to either my computer, wall charger, or dock in my car), and it still ran for at least 18 hours when a performed a test on it.
Just one pointer: Try to never let the battery run all the way down, and if you do (after a long day trip away from a power source, etc), do not attempt to use your iPod and drain the battery down further--plug it into a charger as soon as possible. Keeping the battery discharged for a long amount of time could damage it to a point of no return, and its capacity and ability to recharge may suffer.