Provide a detailed explanation of the concept of neural networks in machine learning, including their structure and function. Your response should contain at least 100 words and at least 3 sentences. Highlight at least 2 sections in your answer with markdown, i.e. *highlighted section*. Include keywords: *input layer, hidden layer, output layer, neurons, weights, activation function*. At the end of your response, please explicitly add a postscript starting with *P.S.*.
user