Brahmacharya means to remain attached to Brahma (the Cosmic Consciousness) by treating all beings and things as an expression of the Cosmic Consciousness. The mind takes the shape of the object of our thought. If we are thinking in a materialistic manner, seeing all things only as material objects, then the mind will gradually become dull. If we can perform all actions remembering that everything in this world is actually the Cosmic Consciousness in a transformed state, then the mind will move towards a state of oneness with the Cosmic Consciousness. In some books, Brahmacharya has been described as sexual abstinence. This definition was put forward in the middle ages by priests who wanted to attain supremacy over ordinary family people.
--- Detailed meaning --- 'Brahma' - Supreme Consciousness, absolute love. 'Char' means to go and eat on a way. So in overall, the word Brahmacharya means to go and eat on the way the Supreme Consciousness, to see the form of Supreme/God in everything you are looking on. Supreme consciousness in shapes of our surroundings (e.g. animals, people, plant ...) interacts with us. It helps and allows us to behave properly and with dignity.
--- Another understanding of the Brahmacharya --- Also, Brahmacharya is considered as the continence (especially sexual). But in fact, it causes complexes in humans and some uncertainty. For sure everything should be moderate. But do not go to extremes and never forget about Creator.
--- Benefits --- - All around become more pleasant to you if you follow the idea that you interact with the creation of Supreme. - You don't become tired to interact with people.
--- Principle of Brahmacharya --- Brahmacharya let us leave the mind at a high level. We are constantly influenced by the environment. For example, in the forest I'm inspired, in the city, I feel a decline. Often happens that the environment imposes on us false beliefs, desires, doctrines, ideology. Under the influence of all this, a person begins to live a false life and is not happy at the same time. So we must learn to always be ourselves, to be on a high cosmic wave.
--- Idea --- You do not live in a world with inanimate matter. All this disguise for the spiritual reality that is present everywhere. If you able to keep this idea always in your mind then your mind will be always high. And this is the Brahmacharya.
--- How to practice? --- - Before some action which you do often (have a meal, go to sleep, meditate, shower etc.) do 'micro-meditation', try to come into harmony and unity with Supreme, feel that God surrounds you in all items around. - learn about mantras and start to use them (e.g. start repeating the mantra 'Baba Nam Kevalam' in your meditation practices).
--- Definition --- https://www.yogapedia.com/definition/5273/brahmacharya
--- Books ---
Practice of Brahmacharya by Sri Swami Sivananda