As far as validity is concerned the premises might be completely and obviously false. The President is a dog. Therefore , the President has eight legs. The conclusion has to be true, if the premises are true. So the argument is valid, even though it has false premises, not to mention a false conclusion.
Form is what makes an argument valid.
If an argument is valid, then the premises make the conclusion necessary . Form makes an argument such that the premises make the conclusion necessary . One can see whether the premises make the conclusion necessary just by looking at the form of the argument . That is why argument form is so important. Look, for example, at the following argument form.