The NAT status column denotes your torrent client's port status:

▶ Green circle indicates Open NAT/Open port/Real IP.

Please note: This does not guarantee that you have a real IP. You could be using a port which is being used by your ISP gateway.
To confirm whether you have a real IP, use the method mentioned here.

▶ Grey circle indicates Strict NAT/Closed port.

This usually means you're either a shared IP user or you didn't forward your ports in the router.
If you're a shared IP user then there's nothing you can do to make it Green/Open.
However if you took a Real IP connection from your ISP, then please do manual port forwarding on your router.

▶ Empty circle indicates the NAT status is yet to be determined. Check back later.

Sometimes you may see outdated NAT status even after forwarding your port properly.
If you want your NAT status to be rechecked, visit the tracker status page and click on the recheck button.