Beginner Question - Building from Source

Morning all

Apologies for the likely basic questions to follow. I am fairly clueless regarding the “Building from Source” workflow. I am currently creating ArchVis type work (Interactable VR games for clients) and have been using blueprints. I have alot of content created. I am now looking into the AR development. I have read up a bit regarding the ARCore for Android and am really keen to try create some basic AR content using Unreal.
I am using an Alienware laptop and running Win10 & UE 4.17 (also have 16/15)
First & most important question is, i need to “Build the engine from source” according to the guide. Will this mess up any of my current work/files? Will i still be able to use blueprints etc.? Im unsure what this means TBH.

There seem to be a fair few steps to follow that are slightly over my head. I am trying to follow this:…etting-started
I have linked my Unreal account with my Github account (never used Github before). Not too sure what the “Clone with this command” part means (i just clicked the “Download or clone”) link. Once i have downloaded the folder from Github from the guide, i click the batch file “generateProjectFiles” as the guide says but i get an error saying files are missing (see image attached). I assume i am doing it completely wrong but cant see where. Was not expecting it to be as complicated xD

Can anyone offer any advice and point me in the right direction. Or if anyone has a video tutorial on doing this process for the ARCore or similar i would greatly appreciate it.

Thanks in advance