There are three basic functions a driver can be performing, driving (operating their vehicles), on-duty (any work including driving), and off-duty (anytime free of work related responsibilities including sleeping).
A driver can be on-duty for 14 consecutive hours, of those 14 consecutive on-duty hours only 11 total hours can be spent driving. After the 14 hours has elapsed the driver must then have 10 consecutive hours of off-duty time (meant for sleeping though they are not specifically required to sleep).
A trucker cannot log more than 60 hours of driving time (not on-duty time) in the past 7 days. But, if a driver takes a 34 hour or longer consecutive off-duty break, the 7 days can be reset. A driver can also opt to limit himself to 70 hours in the past 8 days. Again a 34 hour consecutive off-duty period will trigger a reset.
This is the gist of it. There are a number of other rules which provide provisions for things like bad driving conditions, secondary jobs, breaking up the on-duty hours, etcetera, but this will give you an idea of how much a driver can legally do in one day. Drivers keep a log of all of their activities and any issue with this log can result in relief of trucker duty. The government takes these rules very seriously.