So you have Les Amis and there's nine of them.
First and foremost, Enjolras. Don't be confused by his name. Newbies always like to call him Enjorlas or Eljonras or what have you and nothing pisses off old Miz fans more than that. If you're gonna go off on pages and pages of Tumblr posts shrieking about how he's your favorite and you love him and would die for him and blah blah, you should probably spell his name right. Enjy's blonde, the leader of the group, and infamous for a) not giving two craps about women or flowers or anything not directly related to politics and b) he's sober and god forfend should you offer him a drink.
After Enjolras, we have Grantaire. Grantaire's cynical, drunk and worships at Enjolras' feet. You can either consider this romantic love or that Grantaire admires Enjolras and wishes he were half as passionate. Up to you. But Grantaire does this thing where he signs his name "R". Because in French; "capital R" is "grande R (pronounced: air)" which sounds like "Grantaire." So you'll often see him in fic as "R". (It's why the Enjolras/Grantaire ship is called E/R)
Then we have Courfeyrac. Courfeyrac's proper last name is "de Courfeyrac" because he's from a rich, aristocratic family. But in solidarity with his friends who are super anti-rich, aristocratic families, he drops the "de" and just calls himself Courfeyrac. He's the sexy, flirty one who always has a different woman (or man) on his arm. He's the one who's just as quick to play cards with you as sit down and listen to a lecture on the new anti-printing press legislations. He's also a law student.
Then there's Combeferre. He's a medical student and he's the token smart one. He can match Enjolras in a political debate, and probably outwit him, if he wanted to. He's kind of against all the fighting, but he'll stand alongside his friends. He has ideals and morals and loves his friends and is generally a good guy. Smart, but not nerdy, because he's not afraid to give you an intellectual smackdown if necessary. (He does this to Marius a lot.)
After them we have Feuilly. He's the only one who isn't a rich student. He's an orphan and he barely gets by working as a fan-maker, painting fans for rich people and also painting as an artist in his spare time. Typically obsessed with Poland. He's the poorest one in the group, but a good guy. He struggles a little bit to keep up with the rest of them's intellectual conversation from book he can't afford, but smart enough to hold his own.
Then there's Bahorel. He's not in the musical, because apparently that would be one student too many. But he's always in fic and you look dumb if you don't know who he is. So picture that one guy in every group of guys who's like friggin' huge wnd kind of unnecessarily violent, but also totally sweet (But also unnecessarily violent.) Bahorel's the first one to start ripping crap up and be like "LET'S BUILD US A **********ing BARRICADE, *******!" But then he'll like, tip his hat if there's ladies walking by.
So next there's Jean Prouvaire. He does have a first name and it's Jean. But they call him "Jehan" a lot. He's the adorable, tiny one, who writes poems and plays the flute and stops to appreciate the flowers and always has his head in the clouds. But: when it comes down to it, the revolution is what matters and he will dedicate all his delicate thoughts and time towards it. But also poetry. For example, he's all about his music and his poems and being adorable, but when the barricade is under attack he gets captured by National Gaurdsmen and they drag him over the barricade and put him in front of a firing squad. His lasts words are "VIVE LA FRANCE, LONG LIVE THE REPUBLIC!" because he knows what realy matters.(And then they shoot him.)
Right, so then there's Joly. Joly is also a medical student. But he's a hypochondriac. A hypochondriac is someone who like reads the symptoms for something and then immediately assumes they have the something and even starts to feel the symptoms because they've freaked themselves out so much. So like, he might have a cold. But then decide he has the plague, because oh god, his tongue seems to be swelling up. (Only it's not actually. But it feels like it is, to him.) So, he gets a little bit caught up in things sometimes. Thinking he's ill or someone else is ill. He has a mistress that he lives with. Her name is Musichetta. Hugo doesn't elaborate much on her, but I can only imagine she's especially tolerant and patient, lolol.
And lastly, there's Bossuet. His actually last name is Lesgles. Which at some point became Lesgle. But, and this is where Hugo gets funny. His father is in charge of the post office in Meaux, where his family lives. So because Legle sounds like L'Aigle (which is eagle in French) They started calling his dad L'aigle de Meaux and Meaux sounds like "mots" which is words. So L'aigle de Mots was a nickname for this crazy French priest, Bossuet. So Enjolras and them picked up on that Bossuet's dad is "L'Aigle de Meaux" and made the connection and started calling Bossuet "Bossuet" So in fic you'll see Lesgle or Lesgle or Bossuet. Bossuet is the most common. Oh, and I forgot to mention that Bossuet lives with Joly and Musichetta, and that he's bald, but like 26.
And that's all les amis; Enjolras, Grantaire, Courfeyrac, Combeferre, Feuilly, Jehan, Bahorel, Joly and Bossuet.
...and then there's Marius. Marius is not an Ami. The movie gets this wrong. Marius is a law student and he's friends with Courfeyrac. One day, Courfeyrac is like, "Oh hey, Marius, I have all these other awesome friends and you should come meet them at one of our meetings." and Marius is like, "Well, I have nothing better to do, I guess I'll come."So, Marius comes and they're all like, "blah blah, revolution!" And Marius is like, "Revolution? I LOVE NAPOLEON!" And Enjolras sort of looks at him and is like o.O "We don't like Napoleon here, you stupid, sodden git." So then, Combeferre gives him this really intense smackdown about how much Napoleon sucks and Marius sort of leaves with his tail between his legs and doesn't really come back until the barricade. The movie reaaally wants it to look like he and Enjolras are BFFs. But Enjolras probably wouldn't really remember Marius as anything more than "that guy Combeferre yelled at that one time who really liked Napoleon." Marius/Enjolras is a super popular "I liked the movie!" ship.
Popular ships include;
Enjolras/Grantaire, because lofty sober leader and drunkard.
Enjolras/Combeferre, because lofty sober leader and intellectual right hand man
Enjolras/Courfeyrac, because lofty sober leader and that guy who will take him out to get laid and teach him about how to have a good time
Jehan/Bahorel, because tiny poet and incredibly large violent guy
Courfeyrac/Feuilly, because richest guy and poorest guy
Joly/Bossuet/Musichetta is pretty much canon.