The short answer to this question really is: that's up to you. What I will do however, is talk about what it means to me and how I try and guide people through my workshops and courses.
Using art in spell work and ritual has a long heritage. Often we think of chanting, music or dance as a way of opening hidden portals but visual art can do this too. There are many artists who explicitly used art as an occult practice, such as Hilma Af Klint or Marjorie Cameron. Today there is a growing number of performance artists that are exploring the relationship between esotericism and creativity. Even artists who would never consider themselves to be part of the occult have discussed the spiritual and transformative nature of creating art. I have experienced profound change through using art in my craft and I believe it has made me a more effective witch (whatever effective means!).
While art witches use different techniques and media, I like to recommend when people get started that they begin with art journaling. Art journaling is using art techniques to record time, experiences, thoughts and more in a book. Your work may be literal, pictorial, abstract, whatever you want it to be. Google the term "art journaling" and you'll find a plethora of styles and indeed your own style may change depending on the project. Magickal art journaling is a method of accessing your inner self (where magick resides) through the conduit of art process. The practice can be a random exploration of the psyche through spontaneous actions, or it can be more considered - as part of ritual or spellwork.
Witches can benefit hugely from art journaling as a means of finding the unique intuitive voice that we all possess. The esthetics are not important here, your goal is to go on a journey. From here your intuition takes over. Whether your work is realistic or not, choices are being made by something other than your conscious mind. This is the sweet spot, this is where we find our spirit and soul. This is where I discovered that everything I need or seek is within me.
You need very little to get started with magickal art journaling. A book to work in and some pens are a great start. If you are not feeling inspired or don't know where to begin, I recommend you sign up for my course Introduction to Magickal Art Journaling.