A lot of times folks focus on shielding as a means for defense. I personally prefer a more offensive defensive and personally staying hidden and off the radar as opposed to out in the open shining like a light. One of the methods I use is shadow. Most everything for instance has a shadow, and no one really looks at that or to that or thinks on it. It is quite effective.
So what does it mean to use the shadow? I will simply teach how I was taught and add in some of what I learned over the years. Most people do not realize the shadow is like a different plane. One who stays in the shadows is harder to find on the physical plane energy wise(or impossible depending on skill in it) but has easy access to the physical plane at the same time. Everything is connected to the shadow, even if they do not realize it. Making it quite easy to use the shadow to travel to someone who may be trying to find you for instance and “surprising them” with a bit of nasty of your own. The easiest way to do this is to use a mirror or an actual shadow extending from something. Focus on it and “fall into it” the world will be different and odd on the other side, but your energy body will be masked/hidden. Once in there as long as you stay near the edges you are pretty much safe. Yes the deeper you go into the shadow, the more “things” one may encounter. But they tend to stay away from the edges one can use to enter and travel.
Using shadow to travel. This takes some time and you will make a lot of mistakes. For instance a shadow in the next room, or a mirror, may not be the closet exit point in the shadow. You could end up half way across the world by just moving a few feet and exiting. Fun to use and explore of course. It is a bit like OBE or astral travel, save for it using a different plane as opposed to those one normally uses.
How can it be used to be offensive? No one will really expect one they may be looking for or trying to attack to come from behind and not be detected until its to late (hint: most shadows extend inside ones shielding and can be used to get inside of ones shields as well.) thus making it a really big surprise attack with a nice punch one most likely will not be prepared to handle.
Lastly, what is the shadow? Well the shadow is its own unique realm or plane that basically mirrors ours. It has its own flora and fauna just like any plane. It also has many uses, as well as many dangers if one wanders too deep.