Domain reselling may or may not be something that you should go into. For the most part, you pay a fee each year to be a reseller. From there, you maintain and webmaster your domain reseller website, and try to get customers. If you get enough customers, you will earn more than your fees, and actually gain some profit. But always remember, even if you are a domain reseller of sites like GoDaddy, Wild West Domains, eNom, and Reseller Club, you are still in competition with them as well. When most people buy a domain, they go to GoDaddy, Hostgator, Blue Host, etc... You need to make them go to your site to purchase the domain.
Most people like to get domain names at the same place they host their websites. Thus, you will likely make a lot more money by offering website hosting as well. Website hosting is not easy, and you must learn a lot to be a web host. It can be done, but it's not always a smooth process. There is profit to be made, but it won't happen fast, and it won't happen without a lot of customers.