iptables -t nat -A POSTROUTING -o eth0 -s 192.168.0.0/24 -d 0/0 -j MASQUERADE
192.168.0.0/24 is network behind router (PC) and
eth0 is interface with connectivity. This iptables rule will allow forwarding packets from NAT-ed devices to any IP address.
/etc/sysctl.conf enable IPv4 packet forwarding:
# Uncomment the next line to enable packet forwarding for IPv4 net.ipv4.conf.default.forwarding=1
You can immediately do this with command:
echo 1 > /proc/sys/net/ipv4/ip_forward
Remember to set correct IP addresses and gateways on the NAT-ed devices.