Hi there,
Before I provide a good source to learn TensorFlow code-first, I want to ask why exactly the constraint of not using any libraries?
Other than that, there is a beautiful TensorFlow course that teaches in a code-first approach, meaning you learn by doing. I think this is a perfect way to be introduced to this topic.
https://dev.mrdbourke.com/tensorflow-deep-learning/ 11
It’s written by Daniel Bourke, who is sometimes also roaming these forums 
Hope this helps!