This is the course assignment of Coursera's Deep Learning Course
Instructor: Andrew Ng
This course is one of the best course I have come across in the internet. You may find lots of tutorials on youtubes, article etc. but deep understanding and practical implementation of each process like feed forward propagation, cost function, backward propagation and gradient descent is important. Fortunately, this course does explain everything you need to know about deep learning without using frameworks like Tensorflow, Keras etc. This is mainly for your reference and DO NOT COPY any part of the solutions.
Please use this materials if you really got stuck in the assignment.