Code:
/sbin/iptables -A INPUT -i eth0 -m state --state NEW,ESTABLISHED,RELATED -p tcp -s 0.0.0.0/0 -d 12.34.56.78 --dport 10000 -j ACCEPT
replace eth0 with your external interface device (which is probably eth0)
replace 12.34.56.78 with your external IP
replace 0.0.0.0/0 with allowable IP network ( 0.0.0.0/0 means everyone )