You can connect by telnetting to ifmud.port4000.com, port 4000. Since May 1999, ifMUD has been located at 220.127.116.11 (genesis.epicverse.com) and is maintained by Mark Musante. This may or may not change, so the port4000 address is the safest.
Log in as "Guest" with password "guest" and ask a wizard (the list of wizards can be seen by typing '@users wizards') for help with getting a character. If you are totally lost, type '@holler HELP ME!'.
More information on ifMUD is in the ifMUD FAQ at <http://www.ministryofpeace.com/text/ifMUD/FAQ.html>.
The Interactive Fiction Hall of Shame (ifHOS) is a collection of photos of raif and ifMUD regulars. It can be found at <http://www.davidglasser.net/ifhos/>.
ifMUD's website is at <http://ifmud.port4000.com:4001/>; it contains two web-based clients for ifMUD, though neither of them are as good as a decent MUD client. You can also sign up for a character on the website, though there is nearly always a wizard on the MUD to create one for you.
While at port4000.com, check out <http://www.port4000.com/> for Sadie Hawkins, a band formed of IF people. It is the official band of this FAQ, by the way.