These are tutorials directly to unreal engine ufficial youtube account. I often use them
Getting started with editor:http://www.youtube.com/playlist?list=PLZlv_N0_O1gasd4IcOe9Cx9wHoBB7rxFl
Getting started with level editing:http://www.youtube.com/playlist?list=PLZlv_N0_O1gak1_FoAJVrEGiLIploeF3F
Introduction to materials:http://www.youtube.com/playlist?list=PLZlv_N0_O1gbQjgY0nDwZNYe_N8IcYWS-
Introduction to blueprint:http://www.youtube.com/playlist?list=PLZlv_N0_O1gY35ezlSQn1sWOGfh4C7ewO
From these you can start looking for more vids and tutorial.
This last link is a full documentation of major topic of Unreal Engine 4