You can run a local relay called citrine on Android. nostr:nprofile1qqs827g8dkd07zjvlhh60csytujgd3l9mz7x807xk3fewge7rwlukxgpz4mhxue69uhhyetvv9ujuerpd46hxtnfduhszrnhwden5te0dehhxtnvdakz7qgswaehxw309ahx7um5wghx6mmd9usjfpck if you want to run a personal relay on a PC somewhere there are a bunch of implementations you can use. Getting it connected to your apps on your local network is pretty easy. Accessing it from anywhere is a little harder and there are a few options. There's so many ways you can do it that it's hard to make a recommendation. I think we need more self hosting relay guides.  

 ok, thank you for the details.
I'll check first how to run a personal relay (not Android).
But I'd like also to understand how public relay management works in general and what are the challenges. I want to understand how much of a help it is for nostr in general if I just start a new public relay.
I'm not looking at this to build a business. It's a war effort.