If you are using nntool in matlabl, things are pretty easy. You can check its documentation for how to do. Basically, it will ask you to give a set of inputs and a corresponding set of outputs. All these, inputs and outputs, are the training datasets. MATLAB, would set aside a portion of these data for training and the rest for cross validation. Once the training is done, you'd be given the performance curves as well as the weights of the nn. You can save this network, and try to use it for processing other inputs.
Another approach, if you want to do it from scratch, is gradient descent optimization or other similar methods. A nice tutorial on using the gradient descent and how to check the convergence is explained amazingly by Prof. Andrew in Coursera Machine Learning course.
It is a tool for prediction applications wherever applicable. It will give a relationship between targeted output and all other input parameters and also how the parameters influence the target.