It all depends on the route you want to take.
You can use a hosted service like Wix.com, Shopify.com, Weebly.com, BigCommerce.com. Volusion.com, and many more. You pay them a monthly fee and they will give you a template based store, where you can add products, descriptions, and all the stuff required. You link your payment gateway with them and you're ready to go. It's quite easy. Some of these will charge you a monthly fee + transaction costs, others will only be monthly fee. They range from $10 and up for ecommerce stores.
If you have your own hosting, you can choose to host your own ecommerce store using a number of different software like Magento, WooCommerce, OSCommerce, OpenCart, Prestashop, and many more. Most of these are open source and free. They usually require a bit of work to get it to look exactly like you want, but they may save you money in the long run and be more customizable.
You have a number of choices and it's easier than ever to get an online store ready to go in just minutes nowadays. As long as you have your payment solution ready, you can pick from a number of different options for your ecommerce website.
good luck!