How do you find online journals and magazines and such? I'd love to find more of these on the internet 
The fun part is that there are so many, so you could spend forever looking and keep finding new ones! Most of the big journals are published by large universities (these are the ones most likely to be behind paywalls as well, but not always), but there are dozens that are also just the pet project of one or two people. Basically anyone who can set up a website and an email can start a journal, and many do! A lot of ones from universities, big and small, are student run as well (I'm on the staff for my school's journal, although ours is print only).
I know the most about journals publishing "literary fiction" (I would argue there isn't a hugely meaningful distinction between litfic and other genres but that's a topic for another time), so the majority of suggestions I can give for finding magazines apply best to that. A good place to start is to just search "literary journal" or "literary magazine" and see what comes up. There's also the website NewPages, which has
a list of literary magazines that you can filter to only include online or print publications as well as to search specifically for magazines that include fiction, poetry, visual art, etc. NewPages is intended more for writers to find places to submit their work, but it's also really fun to just scroll the list as a reader and find journals that jump out at you. You could also try and see where your favorite authors have published; they might have it on their website somewhere, and they've possibly linked the ones that are online. You can look in the front or back of a short story or poetry collection you like to see if and where any of these stories/poems have been published before; it's expected to credit all previous publications in your book, and most authors send those same stories or poems to journals before they've finished the book. This might lead you primarily to bigger, more prestigious journals (read: paywalled), especially if the author is an established name, but some of them might be online.
For science fiction, there's a
list of magazines on Wikipedia that marks which ones are online vs. which ones are in print. Many of these also publish horror and/or fantasy as well. The list of fantasy magazines doesn't have its own page like scifi does, but there is a list on
the "Fantasy magazine" page itself that also marks online publications.
Also, if you like poetry, I'm sure you've heard of
The Poetry Foundation. They're a great resource for looking up quick biographies about poets, but they also often have a few poems by each of them! Older poets tend to have more works on there, and you won't be finding "the complete works of X" for any of them, but if you're just looking to sample a few classic works and a few contemporary ones, you won't run out anytime soon.
It seems that the main audience for most of these magazines these days are writers. When you look it up, most lists of magazines are blog posts about where writers should try to publish. I didn't really know there were so many magazines publishing exclusively fiction and poetry until I learned about them from other writers. And I think this is a shame, because, if you find a magazine you like, you will be able to easily access new fiction by writers you might not have ever heard of! And reading a handful of short stories here and there can be a great way to spend more time reading without having to make the commitment to finishing a novel.