Pixelfed

I've started to get into Pixelfed these past 2 weeks but one thing I don't quite understand yet, is what content is getting federated and what isn't. Under "Discover" I can see some trending posts from other instances but most are from the one I'm on and most have barely any interactions in terms of comments etc. I'm a bit surprised, as it's supposedly bigger than Lemmy now but I can see much less content and interactions than on Lemmy. So am I actually getting all the content from instances my instance is federated with, or is it maybe just the specific accounts being followed by members of my instance? And are interactions like hearts getting federated or are they just local?