WHM is the hosting administration control panel. It allows you the manage and create hosting accounts in your VPS. Some functions you can perform include create and manage all hosting accounts, limit accounts disk space, bandwidth, email accounts, email all accounts, change account passwords, check server status.
cPanel is the hosting accounts control panel which allows you to manage the individual hosting account. Functions include create/remove email accounts and forwarders, view website stats via AWstats, view account information such as bandwidth usage, manage domains, subdomains, parked domains, manage and create mysql databases, add/remove FTP accounts, use advanced tools such as cron jobs, hotlink protection, access to pre-installed scripts such as Fantastico.