Alright, first of all, these ratings are placed on my (and other) stories mainly as a guideline. They tell you want to expect, though sometimes, they're overrated, for fear of being persecuted. What I see as 'R', you might see as 'PG'. Just the same, what I see as 'R', someone might see as 'NC-17' and hunt me down. My point is, please understand the guidelines. Here's how the rating system goes:
G - nothing wrong with this. It's almost Disney-esque how innocent this story is. That doesn't mean it's bad, just not offensive in any way.
PG - Some mild violence or swearing occurs, but nothing too offensive. Like watching television, really.
T - for teenagers, mainly. Some violence or sexual themes may occur, but nothing that your mother or father would disapprove of (unless you are brought up very morally, in which case, you may want to skip it).
A - A good amount of swearing, gruesome violence, sex, or other 'offensive' material.
NC-17 - I don't believe that you'll find anything like this on here, but in case of, this means very explicit sex, violence, consistent swearing, and other things deemed 'hellworthy'.
Please, do not let these ratings stop your enjoyment of a story, but do keep them in mind.