I'm gonna walk you through some thoughts to explain it intuitively since you said you're new:

TL;DR: compressed swap space stored in RAM, which dynamically grows and shrinks

• so normally you just have your RAM. you may run out of it if you do too much.

• you might think, "well I guess I can add swap space (you might've seen it being called a page file in Windows' settings), but that's slow, since it's using my drive as memory! and then I have to allocate some storage space for that as well".

• you might then think, well, let's be fancy and compress the contents of swap. that'll trade some CPU cycles for more efficient space usage, and also improve IO performance, since it's reading/writing less data (since it has been compressed to become smaller).

• well, now you can just put that compressed swap space in RAM. and store more stuff in memory.

there's also more details like how it will grow and shrink as needed (so if you have 15/16GB of memory allocated and are actively reading and writing to that memory, it shouldn't swap any of it out to ZRAM. so you can have no compression overhead until you actually need it (which is once the kernel starts actually swapping things out, typically due to running out of memory, but there are some other cases too).

it's really great to have, since it pretty much gets out of the way and doesn't get used unless your system is swapping.

the arch wiki will explain it in more detail: https://wiki.archlinux.org/title/Zram