Hello my name is David, im currently working as an “amateur designer” in some place where they make shirts, pajamas and so. I’ve been using CorelDraw and photoshop in the basic ways and I wanted to know how to make designs like this. Especially the ones that might have some “special effects”. All of this because we’ve got here the plotter machine to print big designs. Thanks a lot for your help and time.
There’s not a lot in the way of ‘effects’, per se. That is just a style of illustration. To do it, you’d have to be able to draw.
However, the obvious question your post raises is, why copy someone else’s style in the first place? Be original.
Hello thanks for your answer. Im not good enough to have a style myself or maybe I dont need to. If you can help me with this regard Id be so grateful. 
There’s not an easy answer to your question. Drawing and designing these kinds of illustrations takes years of practice. It’s not a software trick or an effect that can be applied in a program.
Instead, it’s about learning to draw and practicing many hours each day for many years. It’s a little like learning to play a musical instrument. First, it takes talent. Second, it takes passion and commitment. Third, it takes an enormous amount of practice — literally thousands of hours.
The illustrator who drew your examples might have spent a day or two on them — probably less. However, he or she spent years learning how.
Obviously this requires a lot of painting practice and color matching practice, which can’t be achieved in a day or two.
If you can’t do it yourself - hire an illustrator to do it.
You have the machine - but not the design skills.
Makes sense to me to hire someone who has the skills you lack.
