Introduction to neural networks
3Blue1Brown by Grant Sanderson has a series of 4 videos on neural networks which is easy to watch, fun, and does an excellent job at introducing the functioning of a simple neural network.
What are NN? (19 min)
As you develop your own ML models, if you find that your mathematical background is shaky, 3blue1brown also has an excellent series of videos on linear algebra and an equally great one on calculus.
How do NN learn? (21 min)
What is backpropagation? (14 min)
There is one minor terminological error in this video: they call the use of mini-batches stochastic gradient descent. In fact, this is called mini-batch gradient descent. Stochastic gradient descent uses a single example at each iteration.