So far, i didn’t completely understood about server. But for the information sharing purpose, i am leaving some information that i found. Excuse my quite poor Eng though 
Before get into it quick catch up about what was my issue, What i tried to do is ‘Simulating multiple world’ thing via using server system.
if your goal is likely same as mine and you are about beginner level, you might find some useful informs i hope. 
"Dedicated" or “Listen” ?
Dedicated server is ‘standalone server’ so all player should join to it anyway.
Listen server is somewhat ‘hybrid’ thing. At least one player is bounded with server. That mean, if bounded player(host client) quit the game, server got shut down.
Since listen server is bounded with client or player, you can not launch several servers while only open one client. So for my issue, choice was clear. “Dedicated server”
How should i launch my Dedicated server?
I found 4 ways to launch a server. Launch .exe file’, ‘Command line with Open or ServerTravel command’, ‘Blueprint nodes related with Session thing’ and ‘Check “launch dedicated server” option on your editor’.
I am quite not sure but, Command line and Blueprint way is for Listen server. or at least it may become bit more complicated for launching dedicated server.
And ‘checking option on your editor’ is only launching one server.
So, yes, you should build server to create exe and launching server by that.
And for last, here is some useful links about creating and launching dedicated server.
"How i build dedicated server?"
About network. Even your server will have only one player, the network rule applies.
"So i has server and i know some basics about networking. But i want to launch server without clicking exe file manually"
There is c++ function that execute some file. You can use it to execute exe file to launch a server. And you can even pass some information to opening server.
(Launch a dedicated server during game? - Content Creation - Unreal Engine Forums)
And this is a doc about URL arguments.
(Command-Line Arguments | Unreal Engine Documentation)
Assume that you want to launch server with map named as “ExampleMap” and store some custom values on server like ‘map size’, ‘player name’ or something else, The URL will be as like " /ExampleMap?MapSize=Medium?PlayerName=MyName -log"
After that, When you want to read ‘MapSize’ value, use ‘Parse Option’ blueprint node. passed options will be stored on server’s GameMode class. So get options variable from GameMode and extract value from it 
So, that is about all i found so far.
Hope it helps someone.
Again, sorry for my bad English. Have a nice day.