Hih, Jim,

It is actually pretty easy.  Hit the HOLD button and a little fill-in-the-boxes line appears.  Pick a waypoint with your LSK and it should fill in the hold.  Then you have to set it up.  Your FMC will want to know if it is a right-handed turn or a left, the initial direction, and how long it is, measured in either minutes or nautical miles.  

For example, on my SINCA FIVE arrival at KATL, there are all sorts of holds.  (Atlanta has the world's no. 1 busiest airport, so it needs them.)  I looked at RIPPI and see it is a left hand turn with 314 degrees inbound, and 15 nautical miles.  (That's a pretty big hold.)  You just plug that in: "314/L" and "15" in the miles option below time (it mght default to 1.5 minutes, not sure if I remember for certain.)  It will get put into your LEGS page.

You should see the racetrack on your lateral navigation display.

Your airplane will automagically execute the hold.  Be sure to switch from VNAV to SPEED and dial down to 200 kts. to keep your turns tight and save fuel.  (That's the speed I use; there might be a different realistic standard speed.)  When you get bored (or start to get low fuel) just select the next waypoint as you're heading toward it and you'll exit the hold.

Switch back to VNAV and it will resume control of your speed according to your original entered data.  Holds are fun, and great opportunites for dramatic screenshots, because you can catch the right illumination and bank angle.

You can check out my screenshots here (choose slideshow option if you want). Feel free to leave comments on my home page for your favorites

http://cid-68da1e23ad1ea160.skydrive.live.com/browse.aspx/Captain%20Sim%20757