Difference between using fork/execvp and system call
System also uses a fork/exec... combination. If you do fork/exec yourself you can execute parallel to your running process, while system is blocking (includes the wait). Also system executes the command not direct, but via a shell (which makes problems with setuid bit) and system blocks/ignores certain signals (SIGINT, SIGCHILD, SIGQUIT).
Yes, system() runs the command through a shell, while exec() runs the command directly. Of course, introducing a shell opens up for bugs and exploits.
Edit: of course, the man page provides more detail.