Not sure about the specific problem you are having: is it that you do not know how to configure port forwarding or that you have done so and it does not work. Firewalls...?
Do you have the User Manual?
If not, check this link:
http://www.netgear.com/support/product/D6300.aspx?cid=wmt_netgear_organic
Use the manual to check your setup/router configuration. Verify that you are using the correct ports and that nothing else is blocking those ports.
Work through the setup again and post details if the problem continues. Thanks.