How do I build a good online store on my own?
It is possible to use a website builder or WordPress, but you will get a template web design. In case you want to create something unique, take a look at the projects that suggest a new approach in website building like https://snowfox.tech. It may look quite simple, but can provide you with a fresh idea. Personally I think it is worth trying.
Use Shopify for it! It is so easy to build a great eCommerce website with its help. You can use one of those nice themes for it from https://www.templatemonster.com/shopify-themes.php and get them for 2 dollars each. It is an awesome deal, as for me. What do you think? Check the blog on http://templatemonster.com/blog/save-99-shopify-themes-subscription for some details on it. Good luck with your websites 😉