I designed the snake on this shirt for my RedBubble site, and like all my POD (print-on-demand) designs, it's available on shirts, bags, skins, pillows, etc. My shop: https://www.redbubble.com/people/Okir/shop?asc=u
I didn't come to this type of design process professionally. I'm learning my design chops by creating designs for my shop the site. I bought a Huion digital tablet (not top-of-the-line, but has worked well for me), purchased a drawing/painting app, and then, step by step, learned how to use the programs, and how to work with the POD system.
My first big hurdle had to do with money. I couldn't afford a Photoshop subscription. So I read a lot of reviews, and tried out a number of free or low-cost image processing programs. I found out that some of them, like Fresh Paint, were fine -- but couldn't produce images that were large enough for use in a POD, or were limited in other ways. Eventually I settled on Autodesk Sketchbook Pro, for a whopping $25. While not as wide-ranging in its function as Photoshop, it has served me well.
I had been drawing and painting on paper or canvas for most of my life (I'm in my 60s), so it took awhile to learn how to handle a pen on a tablet surface, and figure out how it differed from regular pens and paint brushes. My first big lesson was when I realized (after creating a posting half a dozen designs) that none of this was going to work if I didn't learn how to do transparencies -- otherwise, all my designs would be boringly square, and the customer could not customize for different background colors. Fortunately, RedBubble had tutorials for that, and there are tons of video tutorials on the internet for every aspect of creating digital art. Once I learned to do transparencies, my designs looked a lot better, and could be printed on more types of items.
I started out doing simple, abstract designs, gradually making them more complex. I also used some of my old images that I scanned from paintings or drawings on canvas or paper. I look at a lot of digital art, daily, including art on RedBubble and other Pods, and gradually realized that I have an affinity for mid-century and modernist design. I also started pinning a lot of my favorite designs to a Pinterest site: https://www.pinterest.com/jeanvengua/ I spend a lot of time just looking, getting inspired, and figuring out what I like. I've never had any academic training in art except for several classes in community college, so I try to approach this process by going at it in-depth -- drawing and painting on an almost daily basis, even though a lot of the stuff I create goes into a folder and doesn't get used.
The Black Snake design came about when I started to realize that complex doesn't necessarily mean better. I wanted to create a recognizable, powerful image that was at the same time very minimal. Periodically I cull designs that I've grown bored with, or that don't seem to appeal. I've started selling some of my designs on Red Bubble, which is great. However, because the POD site purchases the base product materials, handles fulfillment and shipping, the artist gets a very small cut of the profit.
At this point, I don't mind, because I'm continuing to learn a lot about digital design and marketing my work. At some point, I will probably move on. Perhaps I'll look further into the process of getting my surface designs licensed. But so far, working with the POD has been a very useful process.