How can the concepts of black and white magic be understood?
Selecting proper citations from the ageless wisdom takes time and will delay an answer. So I shall here use my own words and perhaps later publish a more grounded and elaborate answer.
Magic can be understood as the usage of energy and the wielding of force. In black magic this is done for the benefit of the separated self, of the personality, and in white magic this is done for the benefit of all, of the united self, of the spirit or soul. Black magic aims at material results and is therewith involutionary: it 'traps' spirit in matter. White magic on the other hand is evolutionary and aims at spiritual results whereby matter is spiritualized. Black magicians usually work on the personality levels of the physical, astral and lower mental planes and white magicians usually do not work lower than the abstract mental plane of the soul.
Sometimes there are clashes between the wielders of black magic, the dark brothers, the dark lodge, and the wielders of white magic, the white brothers, the white lodge. This happened for instance relatively recently where this clash precipitated on the physical plane in the two world wars. In this clash the white lodge was victorious. There was also a great clash in Atlantean times where neither of the two lodges triumphed.
Involution, whereby spirit descends into matter, and evolution, whereby matter is spiritualized, both have their place in a rounded cycle, however wielding involutionary forces during the cyclic period of evolution, in which we are presently placed, is evil.
Evil is basically inherent to the matter that constitutes our planet and solar system. The earth inherited its evil from the moon, which was its previous incarnation, and likewise our solar system inherited its evil from its previous incarnation. There is also cosmic evil.
The overcoming of the pull of matter by spiritualizing it is the goal for men in our present cycle. This is white magic in the larger sense. Every thought, feeling and deed aiming at either material or spiritual results counts in this. In that sense 'every little thing we do is magic'.