Ports are a construct and implemented through memory mapped I/O used by some protocols, such as TCP/UDP, to maintain a persistent connection between computers. ICMP traffic or Ping traffic, however, is session-less. There are no ports one can allow to permit ICMP echo requests.
Most computers will, by default, automatically respond to ICMP echo request (pings). If you can't ping a host machine, it is likely that it is behind a router of some sort. In that case, you must log into the router and explicitly configure it to respond to ICMP echo requests on its WAN port. But doing so will decrease the security profile of your system. Many hackers begin the process of Internet hacking by using a port scan. Typically this is done with an ICMP or Ping request. If they find an ICMP response, they will begin to probe deeper.
The subject is admittedly confusing since the ping program on most computers acts like any other network application, but communicates in a completely different way.