How do I use keras NN to classify data after training?
Once you have a trained model, you can pass new samples to it by using the predict method of the model, which will get you the probabilities of all classes. You than pick the class with the highest probability for each sample as the predicted class:

y_prob = model.predict(new_data)   # Get class probability vector for each sample
y_class = y_prob.argmax(axis=-1)   # Set prediction to class with highest probability


If you are using a Sequential() model, you can also use the predict_classes method, which will get you the same answer:

y_class = model.predict_classes(new_data)