Hi derekmccor
Here is the config for your firewall.
To allow outside traffic :
Access-list name permit (host IP or net range you want to allow )
!! This will create the access list !!
Access-group name in interface (outside interface name)
!! This will apply the access-list to the interface !!
Example
Access-list OUTSIDE-TRAFFIC permit 172.20.20.0 255.255.255.0
Access-group OUTSIDE-TRAFFIC in interface outside
FYI you can do access-lists to allow / deny specifics protocols or services such ping, telnet , etc or any filter any port you want.
Regards ,