This is just a collection of stories set during the series around different characters. The villains are usually random demons or spirits loose in the world who encounter the scouts. A few of the storylines I believe were also adapted into anime episodes.
My favorite of the group was probably either the Ami story where she pretty much drives herself crazy trying to beat a rival student who goes by the penname Mercuris and the one where Mina is jealous of Rei and visits her school. Also, Mina transforms into her Sailor V form twice and uses her disguise compact which we haven't seen since her own series.