You’re totally good to start without a machine! I started making simple sticker designs and flat SVGs for T-shirts, and you don’t need a machine for those. You can test them virtually in software like Cricut Design Space or Silhouette Studio—they have preview functions that show you how the cuts will look.
As for software, Inkscape is a great free option if you don’t want to invest in Adobe Illustrator yet. It’s perfect for learning the basics of vector graphics. Start simple—maybe try some basic shapes and text-based designs first. It’s a great way to get a feel for things!