How i can download the unreal source code from github and what i can do with it. Can i change the engine and add other functions or i can add new codes to API.
With the source code you can make virtually any change you want. To download the source code first go to Epic Games and link your github username (this is a required step). After that head over to https://github.com/EpicGames/UnrealEngine and download the source code. If you want to make changes to the Engine and submit them to Epic then you need to download a Git Client like GitHub for Windows or SourceTree.