it varies a little from version to version, but roughly:
system preferences sharing services remote login (ssh)
* if you are trying to log in but you don't have a real out-there-on-the-net ip address, and the remote machine isn't on your very own lan, you are likely out of luck. you would need to get the person who manages your interface to the lan (your firewall or whatever, likely owned by your isp) to redirect incoming ssh to your machine inside.
no subject
system preferences
sharing
services
remote login (ssh)
* if you are trying to log in but you don't have a real out-there-on-the-net ip address, and the remote machine isn't on your very own lan, you are likely out of luck. you would need to get the person who manages your interface to the lan (your firewall or whatever, likely owned by your isp) to redirect incoming ssh to your machine inside.