Executing as a Daemon allows Snort to operate in the background as a service. It also allows Snort to automatically restart in case of failure. You can activate it by using the -D argument in the command syntax:
# snort -D -c /etc/snort/snort.conf -l /var/log/snort/
Default rules can be downloaded from:
https://www.snort.org/downloads/#rule-downloads
https://www.snort.org/downloads/#rule-downloads