In case you didn't notice, zines are a big deal to John. He befriends Marisol and Diana through them, and writes one of his own—heck, zines are even the way he learns to trust people and connect with others. Without the zines, John wouldn't have gotten to know either Marisol or Diana, and since he's so closed off except when he writes, it would've been pretty hard for them to get to know him, too.
And it's the writing that matters most to John when it comes to his zine. He tells us: "okay. Zines were supposed to look like that, homemade and weird" (1.44) as an admission that his is more low-budget looking than most—but it's the writing that matters to him, so no worries. It's the writing he thinks about, scribbling words whenever he gets the chance. Writing is how he makes sense of himself and the world, so the zine is his outlet for sharing not just his craft, but himself.
When John admits his zine won't change the world, Marisol counters:
"So why bother then, if it's just some half-assed way to waste your time? If you're not committed to having people read what you've written? What have we been talking about all morning?" (2.39)
She believes zines are a window into someone's soul, and hopes that by sharing theirs, they can help people understand each other. Why else take the time to express yourself? Marisol doesn't let people in easily, but she wants her zine to bridge the gap between her and others. She helps John recognize that he wants the same, that his zine is an expression of himself and a way of connecting with people. And since John at least triples his friend network over the course of the book, we're thinking this connection happens.