Hi BnisBet,
(as always!) has some simple to understand and great tutorials to get your started with the basics.
As for the being a generalist and not an expert don’t worry about that at all! Find the parts of the engine or development that you enjoy and focus on that. The areas I personally love and enjoying learning about are anything dealing with Environment art and props, 3D modeling assets, UVs and lightmapping, Lighting, Materials (still learning a lot here all the time!), Landscapes, and generally anything that would populate the environment. These are the things I’m continually focusing on outside of work and learning the ins and outs of. It wasn’t until UE4 that I started having more fun with Particles in Cascade and trying to create some cool effects! I really enjoy learning from others examples and learning by helping others here on the forum and AnswerHub. This has always been the way I learn the most. It’s through other peoples questions that I usually find something that I either hadn’t thought about doing or another way doing something.
Don’t be afraid to ask questions, you’ll notice there are some stand out people here on the forums and AnswerHub that are really helpful at assisting new users like yourself and when you’re comfortable enough in your specialties you’ll do the same. This community is rapidly growing with amazing people who have amazing ideas and are willing to help others! 
If you ever have any feedback on any documentation or suggestions feel free to post in the “Feedback for Epic” section of the forum. We do check this daily and take them serious.
Thank you!