They meet in college.
Her fathers are extremely sorry that they can only afford two years tuition at NYU, but to make them feel better, she assures them that Ohio State University (which has offered her a full ride) has a great theatre program, and she can transfer to NYU in her Junior Year. She's waited her whole life to escape the small town she's from (about half an hour away from Lima) and the judgmental, jealous people in it (exactly like Lima), so what's two more years right? That's what she tells them, and herself, until she eventually believes it.
His mother is ecstatic that he even ends up going to college. After the whole "getting Quinn pregnant while she was dating Finn" fiasco that shakes Lima to its core, he knows that he's headed down a bad path and has to shape up; he doesn't want to become his father. He studies hard his last two years of school, and keeps himself in tip-top shape for football, and somehow manages to land a partial scholarship to Ohio State University.
It's literally five minutes after he got his mother to leave on move-in day when he hears the knock on his door. He opens it to find a pretty brunette on the other side, dressed in a plaid dress and knee-high socks, holding a giant plate of cookies. He's not sure whether to hit on her or ask her where the rest of the girlscouts are.
"Sup?" Is the greeting he finally settles on.
"Hello, I'm Rachel Berry." She extends her hands enthusiastically and he shakes it cautiously. Her energy is kind of scary. "I see that we are going to be floor-mates this year, actually next door neighbors, so I thought I would come and introduce myself. That way if the situation ever arose where you needed to borrow something or needed some company, you wouldn't feel hesitant to come right on over and ask." She finishes her welcome speech with a giant smile, and he stares at her for a moment before he can really formulate a response.
"Uh…thanks?" Yeah, he doesn't think he'll be coming over for "company" anytime soon (because she sounds like she's not into the no-pants-on kind of company), but it's nice that she's being nice. He's not really used to that where he's from. She seems to be waiting for more. "Oh uh…I'm Puck."
"Your name's Puck?" Her eyes light up. "Like in A Midsummer Night's Dream? Like the fairy?"
"Hey! I ain't no fairy!" He's not sure if he was just insulted or not. She laughs.
"No, Puck is a character in a Shakespearean play. That Puck was a fairy." He decides he likes her laugh by the time her explanation ends.
"Oh." He feels a bit silly now. "Puck's just a nickname that everyone calls me. My full name is Noah Puckerman."
"If Noah is your name, then I shall call you Noah." She smiles again before handing him the plate of cookies. "I need to finish delivering the rest of these, but I look forward to spending the year sharing a wall with you!" Puck smirks as she walks away. He figures she'll regret saying that the first time he brings a girl back to his dorm.
Unfortunately for him, a few hours (and a plate of devoured cookies) later, his roommate, a cool enough blonde guy named Sam, arrives, and Puck's just not down for screwing a chick in front of another dude, and also doesn't feel cool kicking Sam out on his butt for the night to get laid, so he typically only brings girls back in the middle of the day, when Sam (and coincidentally Rachel as well) has class. Rachel's roommate, a cheerleader at OSU named Brittney, is home a lot though. He was a bit worried about that, until one day when he's getting hot and heavy, and she comes over to ask him if he heard the gnomes hammering in the walls just now. He tells her yes, and they need to work to keep the dorm running happily, and that seems to satisfy her. He feels a bit bad about that, but he has needs.
The first time he goes over to Rachel's room, it is actually to borrow something. He can't find his stapler, and he has to staple together an essay that's due the next day. He walks in and she's softly singing along to some Broadway song he's never heard of it, and he's kind of captivated. She sounds really pretty, but soon she's noticed he's there and she's got that scarily enthusiastic smile on again, and he grabs the stapler with a mumbled thanks and gets out.
A few weeks into the semester, he comes back to his room to find Sam and Brittney having a hot make-out session in their room. He walks in, sees it, and does what he would have wanted Sam to do in the same situation, leaves. He knocks on the door next door (where he knows Rachel is alone since her roommate is on his roommate's bed) and asks if he can study in there while the two in the other room "go at it". She not only lets him stay, but offers to make him a snack while he works. Three hours later, he's gotten very little studying of his math book done, but knows a lot more about her. He doesn't remember how the conversation started, but he also doesn't remember anyone being so easy to talk to in his life. She speaks like she swallowed a dictionary, and he has to rush to keep up with her, but the way her mouth looks when she's talking and how interesting her takes on everything around them is totally makes up for it. When Brittney finally comes back to the room, somehow he and Rachel have become friends.
Brittney and Sam become official a week later which leads to a lot more time they spend in one of their rooms. Normally whichever room they take up leads to the roommate in that room walking next door to whatever room they aren't using. Puck and Rachel are forced (neither is complaining) to spend a lot more time with each other and despite the fact she's shocked by his language and ability to be truthful about everything, she doesn't think she's ever had such a good friend in her life. He can make her laugh, blush, and think something new all in a span of ten minutes. They're both kind of addicted to each other…just as friends of course.
It isn't until the first time he brings a girl home when she's there (her morning class was cancelled due to a teacher with a wicked hangover), and she comes banging on his door, obviously super pissed and yelling at him that he's an "uncouth, disgusting pig" that he realizes she's got it just as bad for him as he has it for her. He smirks at her, sends the random slutty girl he brought with him away, and tells her to be his girl.
She huffs indignantly at the fact he told her and didn't even bother to ask, but he tells her all he thinks about when he brings girls home now is if her lips would taste better than theirs against his, and she reluctantly agrees, sporting the kind of smile that used to scare him, but now he can't get enough of.
When the second semester starts, the RA implicates a new rule that if you're inside your room (and clothed or in no other way being inappropriate), you should keep your door open to create a floor community. Him and Rachel are still going strong (even though she hasn't let him get past second), and it makes him smile a bit when he passes her room and he sees her through the open door, even just doing her homework. One day, he's passing, and he realizes she must have forgotten that the door was open because she's changing where everyone can see. Even though this is the first time he's seen her without clothes on and he should just be incredibly turned on (and he is…his girl is hot.), his first thought is just how adorable and her it is that she wears underwear with stars on them. That's the day he realizes he's in love with her. (It's also the day that he gets to go a lot farther than second when he walks into the room, slams the door behind him, and tells her what he just realized.)