I think that since you've found and accessed this page that you are already a fan (probably bordering on obsessive, like me) of Sailor Moon. But in case you aren't already a fan; trust me, I will do all in my power to convert you!
Bishoujo Senshi Sailor Moon (translated as Pretty Soldier Sailor Moon) started as a manga (Japanese comic) in 1992. It was then redone as an Anime (cartoon) for the television-viewing population. It lasted five seasons before ending, so the plots get a bit complicated. I'm not even going to try to explain it, there is, however, a very easy to understand explanation of the story line at Project Anime with a more detailed explanation here. Take note, though, that these explanations only cover the first two seasons of Sailor Moon (as shown in the North American version). After that, you can use the links on my links page, or search for websites on your own to provide more detailed plot summaries..
Recently, a friend pointed out that the history links on my page don't lead to any explanations after the first 2 seasons, and she asked if I would give short synopses of the other 3... so I started writing her the short synopses by email... but I figured I'd post them here for whoever was interested. =)
Synopsis of Sailor Moon S (3rd season)
Synopsis of Sailor Moon Super S (4th season)
Synopsis of Sailor Stars (5th & last season)