Trying to figure out how to send Immich download links that work outside my network

I'm new to this so this might be done basic questions. This is my first foray into home labbing and self-hosting.

My goal is to set up an Immich server to host photos of some theater performances that I would like to be able to distribute to the performers and showrunners. I don't want them to have to download an app like tailscale and set something up, I just want to send them a link to download what they should download. It looks like Immich has this built in, but it only works over my own network.

So far I have set up docker for the first time, set up Portainer to give myself a UI for Docker, and set up Immich and all of that has worked. I think the last step here is to expose Immich to the internet with Caddy and give it a URL. I've been able to keep up so far, but this is where I'm getting lost. I know I need to buy a URL from a DNS service. I know I need to install Caddy. I'm not really sure what the steps are beyond that to get everything hooked up and it seems like most of the Caddy tutorials I have come across assume a level of knowledge on networking I do not have.

Any help or resources would be appreciated!