In terms of correspondence, "to know" is generally correlated with air and intellect.
This is the easiest and yet somehow is the hardest. It seems as though everyone and their mother has written a book, created a website, etcetera, about paganism, witchcraft, or Wicca. Books on every imaginable subject have been written for every imaginable reader. There are literally thousands of sources of information on the Internet (this being just one more to add to the pile!). Not all of them agree. Are some of them right, and others wrong? Who says what, and how did they get their information? Who should be believed? I can only answer some of these questions, and only for myself. But, seeing as others might benefit from my conclusions, I've decided to put them here for those who might find it useful.
There are no right or wrong answers on this path. This can be very frustrating. I myself started out looking for what I considered to be "real" paganism - that part of the occult which had survived from ancient times as unscathed as possible. I have since come to realize that very little of what is currently popular in paganism, Wicca, and witchcraft is truly "ancient." How could it be? We live very different lives in this time than in any that's come before us. For example, I very much doubt that what I have access to at my local New Age shop was available to the average pagan throughout history. Times have changed, and so have our religions. And, should I have been able to find something to satisfy my desire for a pristine ancient religion, I doubt it would have been very applicable to my life. I am a very busy person with many responsibilities and little free time. Although my spirituality is a way of life for me, my religion is something I fit in when I can, and that's what works best for me.
The concept of "To Know," for me, means that I need to be careful that I'm aware of the consequences of my actions. I can't know all the possible outcomes of everything I do, but I can educate myself about the practices I perform. Some have told me that when it comes to magick, the best way to learn is by doing. I'm sure that, for many, this is a good way to go about it. In fact, this is probably the best way for some individuals to learn. But I certainly wouldn't go sky diving without knowing how to operate the parachute, and that's how I think of magick. It can be very powerful and very dangerous. I learned this the hard way early on, and realized that I couldn't practice without the knowledge of what I was doing, what it meant, and the consequences it might have. Just like every other religious system in existence, one must learn the basic tenets before one can practice that religion correctly. Such it is with paganism, but herein lies a problem: What are the tenets of a religion that varies greatly from person to person, and has no set rules?
I am still in the process of learning this for myself, as I think all pagans must be. I have a basic idea of what is true for me, and I came upon it by reading about the ideas of others. The internet, books, and talking with others can be a very valuable source (particularly the last). By learning what others are doing, and hearing their opinions, I was able to find what was right for me. Sometimes it's what someone else is already doing, and I can learn from them. Usually, it's a compilation of many different philosophies, theories, and ideas, with a few (or, sometimes, many) changes. I am an individual, and what works for someone else may or may not work for me. I'm willing to give it a try, but if it isn't something I like I reserve the right to play with it until it fits me, or abandon it altogether.
This, of course, implies that I know myself, my goals, my limits, my desires, my beliefs, etc. Knowing oneself can appear incredibly difficult, yet is very simple. How would you spend your time if given a choice? What do you daydream about? What do you dream about? What are your secret hopes? What do you wish was different in your life? Most importantly, what do you hope to accomplish on your spiritual and religious paths? These are part of who you are - you are a combination of your past, your fleeting present, and your hopeful future. The nature of time, as well as the nature of the self and the mind, dictate that we spend our lives in the past and the future, but never the present. Who I am as I type this sentence is not who I am once I'm finished typing this sentence. Time has passed, and I have changed.
If these things are true, can I ever know myself? What is "myself," anyway? Your concept of yourself is unique to you. I see myself as a creature of the past - it is all I know of myself. All I can say for sure is what I have done. Based on that, I can predict what I will do in the future. The "present" will have passed before I can even attempt to analyze my thoughts or actions. (Can you guess I'm a psychology student?) So I base my concept of myself on a generalization of how I have acted in the past, predictions of how I will act in the future, and my thoughts - in this sense, I am kind, I am overbearing in some situations, I am intelligent and funny, I am a bad listener, etc. Your concept of me will undoubtedly be different than my own. My spiritual journey is a path to a goal, but it is also the goal in itself. I desire to be a better person, kinder, gentler, sensitive to others, loving toward myself, aware of what is around me, and, most importantly, happy with who I am. Paganism helps me achieve that goal. Practicing the religion and developing my own spirituality is rewarding in and of itself, and I change along the way.
I also need to know my intent while working magick. I need to sit down and carefully consider what my desire is, who it might affect, how it might affect me and others, and whether I find it to be morally correct to perform a spell to accomplish it. Spell casting isn't a "spur of the moment" thing. It takes time to carefully plan out all aspects of what you plan to do and the outcome you hope to have. When writing chants or other words of power, you need to be very specific in order to get what you while while prevent as many negative effects as possible. For example, if you want to lose weight, you should be more specific than "Goddess, help me to lose weight." How? By developing anorexia? When? Three years from now? What exactly are you going to do to help the spell work, or do you expect your deity to do it all for you?
I've made up a printable checklist to help you sort out your thoughts in order
to write a spell, chant, etc. (You will need Adobe
Acrobat Reader to view it; click here: 
.)
It doesn't include ethical or moral information about deciding whether to
perform a spell or not - your ethics are your ethics, and you need to decide
what they are for yourself. Plan ahead. Failing to plan is planning to fail, as
the saying goes.
To Know Checklist - Focusing Your Desire.
So, I suppose my concept of the meaning of "to know" is four-fold:
You should have a basic idea of magick and at least some information on how it works and how to work with it before you attempt to, otherwise you may end up hurting yourself, or someone you love.
You can read every book every written and talk to every pagan who's ever lived, and you may not find what's right for you in your search - your religion is yours and you can make it into what you want it to be, so don't be afraid to explore and question the popular theories.
Know what you want out of life, religion, and spirituality; know where you want to go, and your path will guide you.
Know what you want to accomplish and plan ahead for success.
"'Know thyself,' said the old philosopher, 'improve thyself,' saith the new. Our great object in time is not to waste our passions and gifts on the things external that we must leave behind, but that we cultivate within us all that we can carry into the eternal progress beyond."
-- Edward Bulwer-Lytton (1803 - 1873)