I don’t know that much about networking and multiplayer system but I just started.
My question is how to make the game continue if the player who create the server quit or disconnected??
If there is no solution is there other way to do that without using plugin??

After doing a bit of searching, it seems like “Host Migration” is what you are looking for. I’ve not personally implemented this, but found this answer that looks pretty solid. Keep in mind it is a little old, so you may need to work through some things. Hopefully this gets you started:

Just to get your head around networking in general, check out this tutorial: