How to open a particular port in ubuntu?

My SoulSeek client Nicotine+ checks my open ports during initial configuration and promts that the one port number it needs is closed, cutting me off frmo about 50% of the users. Is there anyway I can open that particular port for the application to use?

RUnning ubuntu desktop 13.04. I have not manually installed any firewalls, but not sure if its included in the default installation.

Run this on the commandline; it should solve issue: sudo iptables -A INPUT -m conntrack --ctstate NEW,RELATED,ESTABLISHED -j ACCEPT

To do a specific port:

sudo iptables -A INPUT -p <tcp OR udp> <--dport OR --sport> <port> -j ACCEPT

INPUT is the chain for incoming traffic. -p is protocol (either tcp or udp --dport or --sport specify allowing for destination or source port. -j is "jump" and its where you ACCEPT, REJECT, or DROP the packet(s)

Details on iptables can be found by reading the man page. Since you're a beginner you'll probably find this useful: http://www.netfilter.org/documentation/HOWTO//packet-filtering-HOWTO.html