Developing Java / Python skills

TLDR: I need suggestions on how to advance Java skills an what to focus on when doing so. : ) focusing on learning concepts and being able to explain them myself for deeper understanding (no AI pls)

Hello! I'm a junior in college studying CS, interested in Full Stack development. I've only really used HTML/CSS before, but I would say it's at a beginner/intermediate level.
I also took 2 Java classes and the language just makes the most sense to me so far. I really like it and would like to advance my skills outside of the classroom! I only know basic classes/methods and I've learned to use bootSpring APIs to create controllers and repos. I had a project where I had to learn to make a functioning checkout cart and had to make sure that any new customer added would be also added to an SQL database.

I would LOVE to make a project of my own and I have a couple ideas but I also want to expand my knowledge while doing so. I'm not a great communicator, at least not for tech stuff like this, so I worry that I will bomb any interviews if I even get any.

I'm just looking for:

- suggestions on books or methods you found helpful to not only build these skills but to also deepen understanding of what and why i'm doing everything.

- I'm also interested in learning python so many suggestions on that would help as well!!

- Any suggestions of developing interview skills would also greatly help!

- any concepts / skills to focus on as I advance would also be helpful : )

Thank you!!