If you have lots of time, then you can immerse yourself in the subject. There's tons of reading available, e.g. https://gamasutra.com/category/design/ for starters, and while there are designers who only want to design and have others implement their design, I think you can learn the most and have the most control over your projects if you check out some game creation tools and see what you can come up with (start small, baby steps!)