Step 1: The standard icon representing macro mode usually involves a flower and sometimes the letters "MF" (for "macro focus").
Step 2: For quick-and-dirty work, you can use nothing more than your hand to hold the camera lens up to the eyepiece
Step 3: Center and focus
You want to keep things steady and try to center this blob. You'll probably find that you need to adjust the distance between the lens and the eyepiece a bit before your camera will be able to focus properly.
Step 4: Then take a picture
You can, of course, crop the image to remove the black circle (which is called "vignetting", and is a side effect of not spending $100 on an actual lens adapter.)
Step 5: Use a tripod
Step 6: Make some videos
Step 7: Telescopes and more
Thanks to nospleen (Erich Brandeau) for taking pictures of me taking pictures.
(Instructables user davidmerrill used this technique to illustrate his wonderful explanation of how to hand solder SMT chips (http://www.instructables.com/ex/i/0E9564B43CE71029AC23001143E7E506/?ALLSTEPS). But the technique is so useful and little-known that I thought it deserved its own Instructable.)