This season serves as an introduction to the Sailors, and a foundation for the rest of the seasons. During this season Serena brings into play the inner scouts. Amy is the first to join Serena, Raye (2nd), Lita (3rd), and Mina the last. Luna, a talking cat, is sent from the future along with Serena and the other scouts, and teaches them their techniques. Luna sets them on their path to finding the Silver Crystal before the minions of the Negaverse do. Most of the enemies the scouts run into are by pure chance. The fights are dances of uncertainty until Sailor Moon remembers to use her tiara, or Tuxedo Mask gives a saccharine speech reminding Sailor Moon of her tiara. The villains Jadeite, Nephlyte, Zoisite, and Malachite are at war with each other to be in the position of gathering energy. tragically none of the bad guys make it to the next season. The sailor scouts? Sailor Mars, Mercury, Jupiter, and Venus are "killed" in the last battle.

Season Sailor Moon R
Episodes: 47-89
Scouts Introduced: Sailor Mercury, Mars, Jupiter, Venus, Rini, and Pluto.
Most focused on enemies: Alan, Ann, Ruby, Emerald, Diamond, Sapphire, the four sisters Birdie, Catsy, Avery, Prisma; and Wiseman.

As you can see the scouts have quite a handful to deal with. The inner scouts are resurrected but cannot remember who they or the other scouts are. But they get over this lack of memory thanks to Luna. Alan and Ann are aliens from space, who, in order to live, steal energy from the human population to give to their doom tree, which, in return, gives them life. They steal energy by using cardians (M.O.D's that come from cards). Alan and Ann as humans fall in love with Serena and Darien. After a while Ann kidnaps Sailor Moon with intentions of stealing her energy, and Alan kidnaps Darien. However, Ann dies, during a battle, and the doom tree tells them (yes she can talk) that she was dying because they were feeding her bad energy. So Sailor Moon kills the doom tree, leaving behind only a sprout for Alan and Ann to take care of.
Rini is introduced when Serena and Darien are sharing a special moment; Rini falls out of the sky into their boat and asks Serena for the Silver Crystal. With no luck, Rini then hypnotizes Serena's family, becoming her cousin. Darien, Tuxedo Mask, claims that he feels something familiar about her, why wouldn't he? She's his daughter in the future. Rini seems mainly concerned with returning to her own time to her mother and father, Darien and Serena.
Because Rini comes from the future she has a guardian, Sailor Pluto. Sailor Pluto doesn't fight instead is the guardian of the time portal.
Following Rini is the Dark Moon Family (Ruby, Catsy, Avery, Birdie, Prisma, Diamond, Wiseman, Emerald, and Sapphire). Their purpose is to alter the past to achieve global domination in the future. Catsy, Avery, Birdie, and Prisma are turned good by Sailor Moon, Ruby, however, is killed. Which brings into play Emerald. Wiseman succeeds in turning Rini into Black Lady and killing off Emerald, Sapphire, Diamond. Rini is changed back when Serena reminds her of good memories.

Season Sailor Moon S
Episodes: 90-127
Senshi Introduced: Sailor Uranus, Neptune, Pluto, and Mini Moon.
Most focused on enemies: Professor Tomoe, Eudial, Eudial, Sovereign of Silence.

The main opposing force is Professor Tomoe who creates demon eggs that the Witches 5 takes to collect Pure Hearts. Though the inner sailor scouts foil Witches 5 and Tomoe's plans. Neptune and Uranus are basically observers, waiting for the Pure Heart crystals. Nearly all of the scouts fall prey to Tomoe's plans, but their heart crystals turn out to be duds.
After the three pure heart crystals join together, the Sovereign of Silence is awoken, and now Professor Tomoe's main goal is to collect heart crystals for the Sovereign of Silence to revive Pharaoh 90.
Sailor Saturn appears and defeats Pharaoh 90 with the aid of Super Sailor Moon.
They win, and Sailor Saturn dies but is resurrected as a baby. Her father has completely forgotten about his evil past and starts over with his daughter.