difference between nginx and ddns service

[Drake97]

Is your computer's host name "jellyfin"?  If not, change "set $jellyfin jellyfin;" to "set $jellyfin {insert LAN IP};"

I did that and i dont know, i can't get results,

I am going to think with time tomorrow because something is happening and I am not getting it even if I do everything to the letter and follow your indications, I feel that I am close to achieve it but sometimes things do not work out the first time what you want.
I really appreciate your help

Greetings.