Original text and copyright: https://cedric-neukirchen.net/docs/category/multiplayer-network-compendium

This compendium is meant to give you a good start into multiplayer programming for Unreal Engine.

This Compendium should only be used with a base understanding of the Singleplayer Game Framework of Unreal Engine.

Unreal Engine uses a standard Server-Client architecture. This means the server is authoritative and all data must be sent from the client to the server first. After which the server validates the data and reacts depending on your code.

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With the previous information about Unreal Engine's Server-Client architecture and the common classes we can divide those into four categories:

Dedicated Server

What is 'Replication'?

Other ways for Replication are so-called "RPC"s. Short form for "Remote Procedure Call".

Ownership is something very important to understand. You already saw a table that contained entries like "Client-owned Actor".

Relevancy

We have two more important properties for Actor replication.

Non-/Seamless Travel

The easiest way to start a Multiplayer Game is to set the Number of Players, in the Play Drop-Down Menu, to something higher than 1.

Here is a somewhat unordered list of additional resources that could help you learn