From your question it seems you do not understand yet how really neural networks work.
First of all, neural networks are a class of algorithms that fall under machine learning techniques. Therefore, they learn, either unsupervised, supervised or in a reinforcement type of training. This of course require a learning paradigm. In neural networks the most well studied supervised training is the backpropagation method. However, to understand how this work you first need to understand how a network is developed.
A description of what is a neural network and its foundations can be seen here: http://www.doc.ic.ac.uk/~nd/surprise_96/journal/vol4/cs11/report.html
One practical explanation how you can implement a functional network through backpropagation can be seen here: http://galaxy.agh.edu.pl/~vlsi/AI/backp_t_en/backprop.html
If you read these you will probably know enough to answer your question.