Hi, welcome to TPF. I took
@Derrel up on the hedgcoe books and I have done many of the projects contained withing, both film and digital. He helped me gain a better understanding on the basics, exposure, shutter speed, aperture, ISO, composition, types of photography, etc. Very easy to read and when you try some of the projects, it really brings things all together. The thing with you tube for me as a beginner, I had no idea where to start, what was good, etc. Additionally, doing the projects makes photography fun, at least for me, and gets you out shooting.
Your new D3400 is a very capable kit. Start by reading the camera manual. My biggest mistake I made with the D3300 was I shot way too many images in auto. Here's the thing, the camera is stupid. Crap in, crap out. In auto mode, you loose all control of the camera's capabilities, it decides what is best and it's often wrong. Modes (P, A, S, M) are varying degree's of user control. Once you understand the basics of each mode, you will gain momentum. So start there in your manual. If you need clarification, post them here in the beginners forum and you will get answers. Additionally, as an example; you read up up on program mode in your manual, maybe look through a Hedgcoe book on program mode, you watch a couple of you tube videos on using program mode D3400, go shoot some frames in program, and finally, post your sample images along with questions here.
I would also encourage you to read up on the camera's metering system right away as well. spot, center, and matrix. Post questions you have in the beginners forum.
Read up on program mode and metering system. Order a couple of Hedgecoe books.