The video tutorials on the Unreal Engine youtube channel are a good place to start. Just by going through those examples you should already be able to accomplish quite a bit - building a level, creating blueprints, materials, etc.
From there the documentation, answerhub and forums can often give answers to specific questions. While the content examples that Epic provides can be dug through for solutions to more advanced questions or direct reference for solutions.
I think it’s important to have something you’re trying to accomplish. That way you’ll be able to find and resolve specific problems that relate to the work you’re doing. If you’re just trying to learn the engine in a vacuum it’s going to be incredibly difficult, at least I would think so.