You need to package the project. than you can send the whole file to your friend and if you are in a Lan you can play but if you want to play over the internet you need a little bit more Blueprints and the steam plugin.
You can look at this tutorial this works over the internet and lan.
Youtube: Blueprint Multiplayer: Project Overview | 01 | v4.11 Tutorial Series | Unreal Engine - YouTube
Download link: https://forums.unrealengine.com/unreal-engine/announcements-and-releases/asset-sharing/90535-steam-blueprint-multiplayer-project-files