No matter which version of the story you are reading for class (the full unabridged version, or one of the abridged versions), Les Miserables is a complicated novel which integrates the lives of several characters and stories into one. It is definitely a bit confusing at the beginning, but I encourage you to stick with it. If you can make it to the end (and continue to discuss misunderstandings and points of difficulty) I truly believe it is a story that can make a pretty big impact on you.
When I taught this novel, the most helpful thing for my students' understanding was to keep the characters straight. The story weaves the lives of several people together, so all of the background is necessary even though you won't fully see how their lives intertwine until the end. I encourage you to keep the following list handy, as a point of reference:
Main Characters (and all the names they go by):
Jean Valjean (M. the Mayor, M. Madeleine, and M. Leblanc): protagonist; an ex-convict whose conversion leads him to adopting Cosette and protecting her; he is fleeing/hiding from Javert through most of the story.
Fantine: Cosette's poor mother who gave up her daughter as a baby to the Thenardier's and dies before she sees her again; Valjean meets this woman, by chance, before she dies, and promises to take care of her daughter.
Thenardier (Jondrette): antagonist; he and his wife are poor criminals and con artists, spending the majority of the story scheming up new ways to cheat others and make money; they run an inn at the beginning of the book and keep Cosette as a servant when she's a child; later they steal from Valjean and others; their daughters are Eponine and Azelma and Gavroche is their young (abandoned) son; after the battle at Waterloo, Thenardier steals from the bodies of the dead soldiers and in this way, he is able to later con Marius.
Javert: antagonist; chief of police, who spends his life tracking the whereabouts and identity of Jean Valjean.
Marius: a poor student who is a little older than Cosette; his story begins with him joining the Friends of the ABC (and the revolution) but he also meets and falls in love with Cosette; Marius' father was a body on the field of Waterloo that Thenardier robs. He is still alive, and believing Thenardier saved his life, Marius' father remembers his name and instructs his son to find and thank him after he dies.
Hopefully, keeping these main characters straight will help you to persevere through the confusing beginning of the story. If you can make it through, it is so worth it, as this is, in my opinion, one of the best books of all time. I hope you stick with it.