Sailormoon is from the creative genius of Takeuchi Naoko who is responsible for writing most notably the Sailor V manga series, as well as Miss Rain, Chocolate Christmas and PQ Angels.
In both the anime and the manga, the series begins with Tsukino Usagi, a klutzy high school student, who is found by a magical talking black cat with Luna, who tells her she is a magical guardian and must help to find the Mabaroshi no Ginzuishou and the Moon Princess. To help her are other guardian warriors, the second of whom is Mizuno Ami, Sailormercury: a girl genius who discovers she has a power over water. Together they find psychic shinto priestess, Hino Rei, fiery guardian of Mars, the down-to-earth Kino Makoto, a tomboy who likes to cook is Jupiter, and lastly they find Aino Minako, who made a name for herself in Europe as Sailor V, she joins the group as Sailor Venus, while striving to become an idol.
While searching for the 'silver crystal' the girls also encounter Chiba Mamoru. A university student who is also searching. As the series progresses a relationship develops between Mamoru and Usagi who were legendary lovers from the Moon Kingdom: Princess Serenity and Prince Endymion. While the Moon Kingdom romance ended tragically, the two of them come together in Tokyo, Japan, despite being tormented by various enemies through the series' five seasons.
Through R, they discover their daughter from the future Chibi-usa sent back through time to prevent her from the enemies of the Nemesis. They also discover Meiou Setsuna, the guardian of the Time Gate. Then in S, three more senshi arrive, aligned with the outer planets: Neptune, Uranus and Saturn. In SuperS, Chibi-usa returns, and they battle the Black Moon Circus, and discover powers from Pegasus. The series concludes with Stars, where the senshi encounter a wealth of other senshi from other planets, many of whom have fallen victim to Galaxia who is seeking to take control of the entire universe. The Starlights figure prominently in this series, Seiya, Taiki and Yaten from the planet Kinmokousei who are seeking their princess Kakyuu who escaped from Galaxia and fled to Earth. The starlights disguise themselves as men to be pop idols in the hopes this makes it easier to find their princess.
Anime vs. Manga
While the anime and manga follow basically the same thread, the anime is fleshed out quite a bit, with youma/daimon/enemy of the days and extended plot arcs. Sometimes the story varies drastically from the original manga. Some examples below...
The homosexual romantic relationship between the two generals of the Dark Kingdom is only in the anime. In the manga they have a more teacher-student relationship.
In the original series of the manga Usagi uses the disguise pen to transform into a man to fool a bride-youma. She looks very much like Furuhata Motoki when she does this.
Nephrite and Naru don't even interact in the manga let alone develop feelings for each other. Nephrite is killed by Jupiter when she first bursts on the scene.
Not in the manga at all, Ail and An are two aliens trying to feed their tree with the energy of humanity in order to be able to survive. The alien Fiore who features in the R movie, is very similar in style to Ail and An, but the three don't actually seem to be related according to the plot. Fiore manipulates flowers, and Ail and An have their tree, but they summon enemies by animating pictures on cards and bringing them to life by Ail's flute-playing.
In the manga the Outer senshi take part in the end of SuperS, part way through the series they are shown discussing the fact that there powers are no longer active and that perhaps the princess doesn't need them any more. Later on their powers return, precipitated by Hotaru aging from young child to teenager in a matter of hours, and they participate in the final battles with Neherenia. In the anime Neherenia is destroyed by Sailormoon and Sailor Chibi-Moon, then she is re-awoken by Galaxia at the start of the Stars series and sends her mirror-parodies to attack the Outers at an aquarium, which is at the top of a skyscraper. Hotaru is still a baby at this point, baby Hotaru's powers awaken when she is attacked by a mirror-parody and she ages and powers up the Outer senshi, and they help the Inners defeat Neherenia for the second time.