In very basic terms, and why you want to do them:

Attack surface is the ports and services you are exposing to the internet. Keep this as small as possible to reduce the ways your setup can be attacked.

Network topology is the layout of your home network. Do you have multiple vlans/subnets, firewalls that restrict traffic between internal networks, a DMZ is probably a simple enough approach that is available on some home grade routers. This is so if your server gets breached it minimises the amount of damage that can be done to other devices in the network.

If you don't understand these terms, you probably shouldn't be exposing any kind of port on your router. Seriously, not being snarky.

I used to teach multiple levels of Cisco classes, and I wouldn't expose a port these days, I don't know enough.

Instead, I'd recommend using Tailscale on a home machine and your mobile devices.

Using Tailscale, you can also selectively expose a service to the wider world (not just devices running Tailscale), using the Funnel feature.

I'd say it's your safest intro to accessing self-hosted resources from just about anywhere.

Edit: a couple years ago I opened a port helping a friend test something, I forget what. Within hours I was getting hammered with thousands of requests per hour, people trying to break in.

I wasn't worried because of the security we had, but it was annoying, and potentially a massive risk.