Asklemmy isn’t really a place to ask about lemmy, it’s for asking general questions to users of lemmy, jut like you wouldn’t ask for Reddit support in /r/askreddit.

Regardless, this question gets asked and talked about in the !selfhosted@lemmy.world community fairly often, here is a (slightly edited) comment I made a while back.

You will need a domain name, you can buy one from a registrar such as hover or namecheap (for the love of all that you consider holy do not use godaddy).

You will need a way to expose the server that you set up via port forwarding or similar on your network.

You will need to set up DNS records on the domain you buy to point to your home IP. You may want to figure out a different way to avoid just handing that information out, cloudflare can help with that. You will want to make sure the DNS records get automatically updated if your IP address changes, which is not uncommon for residential ISPs.

You will need to figure out how to get an SSL certificate, Let’s Encrypt will issue them for free, cloudflare gives you one if you use them as a reverse proxy.

Some of this would likely be easier to do on a cloud provider like digitalocean or linode and could be done reasonably cheaply.

These are all common things for setting up any website, so lemmy docs won’t cover them. In addition to those (this answer was just addressing “how to get a URL”) you will need to install and configure lemmy, lemmy-ui, postgres, and pictrs somewhere (the join-lemmy docs cover this well).

If you want your instance to send emails you will have to figure out how you want to do that (too many options to cover in this answer).

When 0.18.1 gets released if you want captcha you’ll probably have to figure out an mCaptcha provider or set that up yourself.

Not to mention thinking about backups, high availability, etc, etc.

Best of luck.