I use two microbiology and mycology books I bought on OfferUp for $10, YouTube and papers. The vast amount of my learning comes from breaking larger technical goals into a series of smaller hands-on projects and then troubleshooting my way through. It's hard to give general advice on synbio since it's such a broad field and my journey principally involves a focus on fungi. In my case, I learned to grow all kinds of mushrooms and fungus at home. That lead me to learning DNA barcoding of fungi which has now lead me to DNA transformation of fungi. Feel free to send me more info about the direction you want to head in and I'd be happy to give you some feedback.