In general, slapd is run as follows:
/usr/lib/ldap/slapd [option]
Because slapd listens on a privileged TCP port number,
you need to be root. For example:
su
/usr/lib/ldap/slapd -f myslapd.conf
slapd will automatically fork and detach itself from its controlling terminal and run in the background. Any of the options given can be given to slapd to point it at a different configuration file, listen on another port, and so on.