since u are new, I know that feeling cuz I had it once
so focus on what Im going to say right now
-to know ur OS bit, just right click on My computer and U should know
-you got the launcher , just install it in ur system, and then choose the unreal version to download
-then after u downloaded it, I highly recommending to watch some Awesome tutorials from Epic games that will teach u how to master this power tool starting with this one:
Intro to the UE4 Editor
then be on fly to choose any course provided here
Zack parish did well through this awesome tutorials and other technical writers at epic games
best of luck