Just have a simple question where can I go to read up on using Null interfaces so far the sites I've pulled up are not very helpfull....thank you in advance
What seems to be happening on your router is it looks like you are peering with RIP to whoever this router is connected to on the fa0/0 interface and you advertise the route for 18.104.22.168/240 to that peer.
You need to advertise this route so any traffic destined for 169.176.124.x/28 will be sent to your router. 169.176.124.x/28 is a NAT pool so it doesn't actually exist on any interface as such. But you need to advertise it so you add a static route for it and redistribute this static into the RIP process. But even though it is not a subnet that is actually configured on any physical interface you need a next-hop so you use Null0.
Now you have "nat outside" on the fa0/0 interface. With traffic coming from outside to inside NAT happens before routing. So a packet arrives for 22.214.171.124 and you have this entry on your router
ip nat inside source static 126.96.36.199 188.8.131.52
so the router translates 184.108.40.206 to 220.127.116.11 and forwards the packet. Note that if routing happened before NAT the packet would be dropped because the router would route the packet to Null0.
So that is why you have a static route pointing to Null0 for this subnet. Why you are tracking the reachability of it to be honest i'm not sure, maybe someone else could explain. Tracking the reachability is a test to see if the next-hop is still up but Null0 will always be up as far as i know as it is a logical interface.
Hope this makes sense.