Most routers have a feature to assign static IPs to a specific MAC address. You can also tell most devices to try to take a specific IP instead of using DHCP.

There are multiple ways to set it up, but it’s very possible to set a specific device to always have the same local IP, which is usually the first step to many self-hosting scenarios.

You can either set a DHCP reservation in your router, or manually set the IP on the device.

When I say private IP, I’m referring to the internal IP e.g 192.168.1.X

Means internally I just go to the domain without having to remember the IP I set.

Edit: i see now they're talking about private IP, but in case you want to learn about getting a static IP for other things...

Many ISPs will give you a dynamic (changing) IP rather than a static (unchanging) IP. Just check your IP once a week for a few weeks to see if it changes.

There are some services that get around this by checking your ip regularly and updating their records automatically. This is called a dynamic DNS provider (DDNS). I used to use "noip" but since then there are quite a few like cloudflare DDNS.

Beyond that you just would want to make sure your router or whatever device is assigning IPs on your network to give a static assignment to the server. Assigning IPs is handled by a DHCP server and it would usually be your router, but if you have a pihole you might be using that as a DHCP server instead.

Between DDNS and DHCP you can make sure both your external IP and internal IP are static.