It looks like you create a macro with a targeted spell, like a heal, and in the Target box where you'd normally type a name you put %v.
Then if you hold your mouse over someone's name in the group or raid window and press the key for that macro it will cast the spell on them.
That's the best I could figure out from a quick test.
Not sure how much use it will actually be if you're using most 3rd party UI's since you probably already have click to cure and some heal/spell buttons on the raid/group windows. If you're going to have your mouse over the group window anyway it's faster just to click the heal button.