If you double-click somewhere on a map, you can then click on "link to this page", and pull out the "ll" parameter:
...&ll=41.631867,-87.138062&...This is coordinates that you clicked on. You can copy-and-paste this into the Google Maps search box, which will make a flag pop up there.
You can add some text in parentheses, and that text will be used in the pop-up description.