I would strongly strongly strongly recommend starting with karpathy's from 0 to hero neural networks youtube course - it starts with building a tensor library and back propagation, explaining it in a way that finally clicked for me https://www.youtube.com/playlist?list=PLAqhIrjkxbuWI23v9cThs...
jeremy howard also has a fantastic video that is more around how to use LLMs and such called a hacker's guide to language models - https://www.youtube.com/watch?v=jkrNMKz9pWU&t=607s
as i've dove more and more into it, i would strongly recommend trying to run things on your local machine too (llama.cpp, ollama, LM studio). that has helped me fight that feeling of like "are we all just going to be open AI developers in the end" and made me feel like you _can_ integrate these things into stuff you build by your self. I can't imagine how fucked we'd all be if llama was never opensourced. being old does not mean that you can't continue to grow, and remember that it's okay to feel overwhelmed about all this - many people are.