well, I took a class back in college with an Old School professor. He's the one who drove the class that way. I just enjoyed the process. But there are a lot of tutorials on the internet about writing your own NN. I think the first algorithm that I ever wrote regarding ML was k-means [1]. Start there and see where it takes you:

https://en.wikipedia.org/wiki/K-means_clustering

Look at this project I have used it:

https://github.com/victorqribeiro/groupImg