if he is talking about a dynamic ip not a local area network ip for sure he can ask people to see his site via static or dynamic ip from anywhere
in case of dynamic ip he should give them his ip every time he wants them to try seeing it...but...
if the dynamic ip is leading to his router ... and his pc is a computer that has a local ip
then he must go into the router settings to lead port 80 to the local fixed ip say like dmz leads to 10.0.0.3 so as to be seen via internet
this can and must be done into the router firewall and virual servers in the advanced settings
if he is set correct and port 80 is not blocked by any security prog,.. then he can be seen via internet as a website..
u can try the following
have ur ip lets say it is xxx.xx.xx.xx
go try ping that ip from an outside pc ..
if u can ping it then u can be seen from outside
if u try to put ur ip in the browser from outside http://xxx.xx.xx.xx
and it leads u to ur router it will ask u for a username and a password that are the router or the windows id and password but mostly the router
if u can reach ur router from outside then u just need to deal with the virual server settings to point ur dms to ur local network ip of the server..
if not then ur port 80 is blocked for some reason ..