your first hurdle is installing a lemmy server locally. this is a mission on it's own, and I can be of zero assistance here.

your second hurdle is enabling port forwarding and making that server accessible from the internet. I'm going to assume you know how to do the 2nd. port foward dot com if you don't.

your third hurdle will be setting up dynamic dns. again, lots of choices here, and different tiers of service/support. I'm assuming this is enough to point you in the right direction, and your home router likely has built in support for a few providers.

I recommend tackling these hurdles in order, but they don't have to be done in order.