help designing merch?

Krita is the free software I use for drawing that has a lot of Photoshop type options and versatility to it that you might find helpful. It's also available as an app for tablets. I find its text tool sucks though, so I'd also recommend checking out the other free graphics software Gimp. Both probably aren't the more intuitive for beginners, but they offer a LOT.

Also the website Canva is great for just playing around and testing out design ideas with ease. I do lots of fun graphics there for stickers, flyers, banners, party decor, web assets etc.

Edit: Another benefit to Canva is that it's a vector program which means that scaling your designs to meet printing requirements is a breeze.