Seriously, it's not that hard. The big two are Archive of Our Own and Wattpad, but which one you prefer depends on what you're after.
AO3's tag system is a lifesaver. You can filter for specific pairings, tropes, anything. The writing quality tends to skew higher because it's run by fans and has a strong culture of feedback. I find the best longer, plot-heavy fics there, especially for less common dynamics or AUs. The downside is some new fans find the interface a bit intimidating at first.
Wattpad is where a lot of the viral hits start. It's more social, feels like scrolling through a feed, and the stories often have a very immediate, conversational style. You'll find tons of the classic 'reader-insert' stories there. The search function is clunkier, so you might have to wade through more to find something you like. Honestly, I keep tabs on both.
Twitter and Tumblr are crucial for discovery though. Authors promo snippets, artists make moodboards, and you'll hear about the latest fic everyone's losing their minds over there long before it hits the big sites.