It's pretty simple, really..........
Step 1) Do a search to see what suitable domain names are available.
Step 2) Purchase webhosting that offers a turnkey online store, or the ability install an eCommerce script by an installer such as Softaculous.
After that it's basically just a matter of learning your way around the script + adding products to it for clients to buy + pictures to accompany them. You may also want to consider Online Advertising so people know the online store exists.