Luckily in 2020, there are tons of websites that will help you start your business online. Etsy, for example, is a great place to sell art and handmade goods, among other products. Digital artists, on the other hand, can look to websites like Redbubble to sell their designs.
That being said, you don't need a long-term business plan for your gap year. If you're looking to make some quick cash instead, you could create your own shop on sites like Depop and Poshmark, which allow you to make a business selling your unwanted clothes and belongings.