Masyadong broad yung "Graphic Designing"
Siguro yung maisasuggest ko sayo, familiarize yourself with adobe softwares (PS, AI, ID, AE, PR, LIGHTROOM, etc.)
Study every tool, kung pano sila gumagana at ginagamit.
Ngayon, kapag alam mo na, study about tips and techniques kahit sa Lynda.com or kahit sa yôutubê lang. Maraming Designer na nagsheshare ng experience, tips and techniques nila. What's important is mapanood mo sila kung ano yung problema nila, and pano nila yon sinosolusyunan.
After that, tsaka ka magsearch ng "Tarpauline sizes", "How to design a Tarpauline using Photoshop", etc.
Also, here's a link para sa account sa lynda.com from our brother/sister LuckyPs:
https://phcorner.net/threads/607569/#post-10088842
Kung wala kang internet at gusto mong isave for offline use yung mga courses sa Lynda, here's my tutorial:
https://phcorner.net/threads/608932/
Hope this helps.