Each Unix task starts as a process with a unique process ID (PID). Processes can be started by the system as daemons or by users through the shell. The 'ps' command lists running processes while 'pgrep' searches for a specific process. Processes go through three stages - fork, exec, and termination. Signals are used to communicate between processes and the 'kill' command sends signals to terminate or suspend processes. Cron executes periodic tasks on a schedule, while 'top' monitors system resources and processes.