The Rules are very simple and must be followed.
Please put a rating in your title. G-NC17
Please put an updated date on the title.
If Slash Please put pairing in the title
Here is a description I got from Wikepedia
G - General Audiences
All ages admitted
PG rating symbol
PG - Parental guidance suggested
Some material may not be suitable for children
PG-13 rating symbol
PG-13 - Parents strongly cautioned
Some material may be inappropriate for children under 13.
R rating symbol
R - Restricted
Under 17 requires accompanying parent or adult guardian.
NC-17 rating symbol
NC-17
No one 17 and under admitted.
Just saying what age group the particiular work is aimed at. Like for instance you're writing a fiction that has graphic sex scences, you explain about every detail then that would be rated NC-17, if you have it mentioned and somewhat detailed, it would be R. If it has none of that, hardly any violence then it would be G. I hope that helps you understand it.
thats all happy writing..