There are two requirements.
One, the greater-than sign (>) Must have a space between it and the text.
Two, you must press the "enter" key to separate the previous line from the one you are trying to indent.
(Enter)(>)(Space)(Text)
Remember:
If you have multiple lines, you'll need to indent them all for the green line to appear before them.
If the preview shows you your answer or question has a green line, and it doesn't, you can always click "edit" and fix it.
Example:
This took me awhile to learn; I have all of you beautiful people to thank.
Visionary OrangeWigMan, on learning how to eat without assistance.
Example on how NOT to do it:
Crap, that dude has problems.
> Assistant to OrangeWigMan
