Assuming that you've got everything being forwarded through your modem to your OpenWRT's "WAN" port, then you just need "normal" port forwarding.
Here's a couple references on how to do that:
Assuming that you've got everything being forwarded through your modem to your OpenWRT's "WAN" port, then you just need "normal" port forwarding.
Here's a couple references on how to do that: