Each definition of magic/k is in the eyes of the user, each person has a different personal one.
To me, its the bending to the betterment of my world.
Its based on your personal belief, no one can prove to you that a spell has worked, nor can you to anyone else. If you don't have faith in your own ability you will not be successful in this craft.
Spells are ritualistic, and somewhat entertaining, they are used for a quite a number of things, depending on belief, they can be used for prayer, postivity, negativity, healing, luck, personal growth, illusion, protection, possibly anything you can think of within the ranges of what is possible on the physical and within common sense.
Paganism in itself is a broad term, which can define people who believe in old age Gods and Goddesses, but, in a way like magic, the definition is in the practitioner.
Wicca is old Pagan beliefs brought into a bit more organized religion set.
You can have any belief and still practice, it just matters what your belief means to You.
Colored magic terms are slightly controversial, in a sense, it is a way commonly used to define magick done for positivity(white) or negativity(black) but, its growing out of the age, as it does give a bad insight.
The practice is with the practitioner, this way is a broad way from people with all sorts of different practicies, voodoo, shamanism, witches, druids, you name it. It would take weeks to explain, everyone is still learning.
Which is why three of the most common words you'll hear from here are
Now, if after this your interested in learning, you would start with the Basics, a list which can be found in the general forum or via Google, though it can differ on which practice you want to learn.