OK!
We are all basically defended from the first Mahou user, Merlin. He studied this power from monk, and managed to master it after years of study and training, using almost physical energy and vitality to bend the nature's to his will. He also found that using Intruments such as wands were able to channel this power.
That's the origin.
"Wands, the basic weapon any Kisei possesses, allows them to channel their chakra to perform techniques and use Mahou and certain Ninjutsu without the requirements generally associated with these, instead using verbal commands known as incantations or, in some cases, movements."
These wands are made from the wood of the Jubei Tree, and has components such as unicorn hair or phoenix feathers to amplify and augment the channeling of chakra.
That is the tools we use.
We use chakra through our innate ability to cast "spells" which is a way to use special Ninjutsu techniques through a combination of movements and vocalisations. Although some can do it without movements or speaking. That release Mahou chakra. These can be classified into different forms of spells, charms, transfiguration defense against darknow arts and even dark arts. There's even more advanced Mahou called leggilimency and occulememcy.
There are different levels of students and teachers, as well as light wizards and dark wizards.
I think that's everything