Reseller hosting is nothing but sharing your space and bandwidth and host multiple domains. The domains may be split up either for multiple sites hosted by the same person or in case of business environment for their own clients. The reseller account holder will have control over the space that is being shared and the bandwidth that is being allotted for the user while website hosting. The number of accounts that you can resell will depend upon the plan that has been chose. The plans vary from one web host provider to another. There are some web host providers that provide reseller accounts alone while some host providers give reseller accounts along with single account.
When you create a sub account you will be getting a separate control panel for each which helps the sub account holder to access the files independently. There are several plans available for reseller accounts you can choose the one that suits you best and as per your requirement for the number of accounts. You can choose over a regular account if you are hosting single website. You can choose a reseller account only if you are re selling sub accounts to others. If you are going to hold multiple sites for your personal use then you can look for other options like VPS or a dedicated server.
Some web hosting companies are specialized in reseller hosting. You can choose such companies for better offers in case you are planning to purchase a reseller account. You can always modify the bandwidth and disk space allotted for a reseller account so that you can check for other website hosting. Initially you can allot minimal plan for reseller accounts and increase them accordingly as per requirements in future. Reseller accounts may be helpful if you are running a web development company. You can offer website hosting as an offer to your clients which will be an option to attract more customers.