What more is there to explain? The instructions are quite clear I believe. The meditation is explained step by step in an easy to understand manner.
If you cannot understand the instructions it's safe to assume you are not yet ready for this meditation.
The meditation requires advanced visualization and is quite an advanced meditation in general, get familliar with less advanced meditations first and practice visualization.
Good meditations to work on daily before doing this meditation are:
http://www.angelfire.com/empire/serpent ... nergy.html
http://www.angelfire.com/empire/serpent ... nergy.html
http://www.angelfire.com/empire/serpent ... Queen.html
http://www.angelfire.com/empire/serpent ... n_One.html
Also, I believe the single serpent meditation and the twin serpent meditation work very well in conjunction, with that I mean when you work on both daily it amplifies both meditations.
These meditations work to open the shushumna and the Ida and Pingala, the main Nadis of the soul, they also greatly empower your energy flow and your mind connection to your energy, but they are quite advanced and thus don't just hop into them without doing enough preliminary work.
Needless to say you must have opened your chakra's already before doing any of these meditations. If you enounter any blockages in the energy when attempting these meditations I listed, that's a sign you haven't opened your chakra's enough yet.
Energy tends to get stuck below the chakra that is blocked, so if you feel energy getting stuck in your throat, it is your 6th chakra that is blocked. If you feel it getting stuck at your groin area it's most likely your second chakra that's blocked.
Energy getting stuck can cause problems, which is why you need to open your soul first before attempting to empower it through those powerful meditations I linked.