In Dennica/ Daystar, witches and magicians are descendants of magical being such as samodivas, villas, rusalki, etc. Some people, born on a Saturday can use magic too, but their powers are limited. Witches are separated into three types and are more powerful than magicians.
The three types are - blood witch, mirror witch and witches of sense. The blood witches are the first, fourth, seventh daughter and so on, the mirror ones are second, fifth, eight and so on, while the sense - third, sixth, ninth and so on. Blood witches are the most powerful, mirror witches are the most gifted, while sense ones are the most dangerous.
* A witch of sense has the ability to free people of curses, to read and control one's mind, control earth and wind, to see people's past, take away their pain, etc.
* A mirror witch is gifted with seeing curses put on people, healing, potion-making, controlling earth and water. They can bless people with fortune and good luck, make one fall in love with them, but also create powerful poisons.
* A blood witch main task is to protect the family - she can sense when a person from the bloodline is in danger. They can curse people, read one's blood, control fire and earth. They can also freely communicate with the spirits of dead relatives.
Magicians, for the most part, are based on Bayan Magesnic(a Bulgarian mythical figure) and Koschei the Deathless. Koschei is one of the most prominent figures in Russian fairy tales, with his role always being antagonistic. Magicians are the ones who came up with the way to be "immortal".
However, this is in Suntolia, Karet and Volniya, which are the three main states where the story takes place, and even between them, there are some differences. Other nations/countries/cultures have magic systems on their own, with similarities between closer ones.
I wouldn't say it's hard, most of it is written so it's easier to be studied by witches, as it is a lot. However, what matters is the individual that is practising. With generations, the connections between you and your supernatural ancestors wears out thus you aren't going to manifest any type of power, or you'll ever find out about your potential. Or you'll want to learn. Over the years the number of people, who practice magic in the land, magic that makes them worthy of being called a witch or mage has decreased rapidly under different circumstances.
A thing to do is, have a separate file, where you write down and develop your magical system, where you write your references to real life, if you have ones, so you can go and check if everything is aligned. Also, go back and reread your stuff, so you can avoid plotholes.