You will have to learn:
-a 3d program (blender, 3ds , maya)
-photoshop or gimp
-probably also a tool for audio editing
I would recommend you to start with the official tutorials on youtube and after that directly start do develop your game -> during the development process you will have questions which you can post here into the forum or answerhub -> we are always here to help 
Some good resources:
https://docs.unrealengine/latest/INT/
https://wiki.unrealengine/Main_Page
https://wiki.unrealengine/Videos