If this is a question about the sorting algorithm, I have no idea how that works. I think it does use up/down votes, but I don't know how.

I think what people are often referring to is that there isn't anything like "karma" from reddit. Your total score doesn't impact anything.

Upvotes make a difference for the "Top - X time" sorts. "Active" (which I believe is the default) is unrelated to upvotes on the post and is based on the discussions going on in the comments.

The sorting algorithm is still a bit of a hot mess but slowly getting better. To my understanding yes, Upvotes and Downvotes do make a difference.

Afaik, if you're on the webpage of an instance, up votes and downvotes don't push things up or down to a viewer. For that, you need to hit another button to "boost" it up, and it only works for ups not downs.

But that's just what I understand from seeing people talking about it; I use Liftoff and it integrates the upvote and boost buttons so it is functionally no different than Reddit, in so far as it looks and feels to the user.

The "Active" and "Hot" sort methods still use the votes to gauge how high or down they appear on the page, but with much less weight than the "boost" option has.

They're talking about Mastodon, where there's no algorithmic feed and likes are only visible when you focus the toot, and so "likes" are kinda useless, only retoots. Lemmy is different, likes matter here.

This is false. On Lemmy, upvotes and downvotes are the backbone behind the Hot and Top feeds.

The only ones where it doesn't matter as much are in Active, which is based on comments.

They do matter, but they are still tweaking the algorithm

Very much wrong:

Lemmy uses a voting system to sort post listings. On the left side of each post there are up and down arrows, which let you upvote or downvote it. You can upvote posts that you like so that more users will see them. Or downvote posts so that they are less likely to be seen. Each post receives a score which is the number of upvotes minus number of downvotes.

You can also see further down that most of the sorting algorithms do take votes into account in some way.