I don't really understand the alogorthm stuff, but for reference, what exactly does the frequency setting change?

I'm perfectly fine with the way it is by default and don't wanna rock the boat, but I figure there's no harm in knowing about it. Is it just like decreasing/increasing a default flat rate of time between SRS levels (although I'm not even sure if this app is like Wanikani where there's flat set rates to begin with as opposed to something I can't wrap my mind around the specifics of like Anki FSRS, which I'd also be curious as to what the difference between FSRS and sm2+ is), or is it more complicated than that?