The cron facility consists of two programs. (There is no individual program called cron, which is the overall name given to the facility. If you execute man cron, however, you will see the manpage for crond.)
This is the cron daemon, which is the process that executes your instructions. It starts at system initialization time and runs in the background thereafter.
This is the cron table manipulation program. This program gives you access to your cron table or crontab file. Each authorized user may have his own crontab file to run commands and processes on a regular basis.
The cron daemon wakes up every minute and examines all crontab files, executing any commands scheduled for that time.