They're both software front-ends for thread-based uses of the ActivityPub protocol.
Basically, they both deal with the same information presented by the servers, they just handle it differently. The main difference for a user is the interface. Think of how the web client for Gmail is coded differently than the web client for Outlook, despite using the same email protocol.
Does that mean I could use kbin as a frontend to access Lemmy? I'm trying to figure out ways that I can help lessen the load on the lemmy.ml instance since that's the one I joined
Kbin isn't really a "frontend" in terms of being just a UI to access a Lemmy instance. Kbin is a different federated app, like Lemmy, Mastodon, Pixelated, etc. What makes kbin uniquely similar to Lemmy is that it's UI is community/forum oriented like Lemmy's is. And it's supposed to be compatible with Lemmy federation-wise, so you can subscribe to Lemmy communities from a kbin instance. A few days ago kbin was like maybe 2% of the size of the Lemmy community though, so a lot of what you'd do on kbin is subscribe to Lemmy communities and talk to Lemmy users. I decided to just use Lemmy natively to eliminate the possibility of incompatibility.
A kbin instance though would be a different instance, and you'd need a new account on it to use it. And if you want to reduce load on lemmy.ml really all you can do is use Lemmy less or abandon this account and create a new one on a less busy instance (either Lemmy or kbin). But honestly if lemmy.ml is working, I'd just stay there. With the crazy flood of new signups, server hopping and creating dupe accounts is as likely to make this worse as it is to make them better. You'd also lose all your subs and post/comment history. There is a ticket for account migration but it's not done yet so you'd truly be making a brand new account with no link to your existing one.
Thank you for this detailed explanation. Account migration is something that was top of my mind trying to figure this all out. Good to know the current limitations, but glad this is on the radar. I’m working on building my own instance so it isn’t an issue for me, but easy options for account portability will help with adoption. Controlling your own online presence is a motivation for a lot of people.
You can even interact with Lemmy posts from Mastodon instances! This federation stuff is pretty wild, but it's super exciting. The combination of smaller servers reminiscent of early internet with the ease of use and standardization of modern web apps has such potential to wrestle back the internet from massive corporations.