Could you explain this for me?

Assalamu alaikum. I've been trying to get back on track with my deen, and I'm a bit clueless about the basics. What exactly are the core beliefs and practices in Islam? Also, with Ramadan coming up, this will be my first time actually preparing for it properly. Any tips on how to get ready, especially for the fasting and spiritual side? I'd be so grateful for any advice.