If you have a copy of the motion papers against you, but just got them now after the motion was granted and never got them before, you make an immediate motion to the court, to vacate the decision for lack of service of the motion, setting a new return date and giving you time to file responding papers.  Your motion will be stronger if you can explain why you believe you'll be able to defeat summary judgment if given the chance.

A summary judgment motion says that based on facts that nobody can really argue about, the moving party has to win, as a matter of law.  You resist that motion either by showing that there really is a genuine dispute, about one or more of the material facts, or by showing that the legal reasoning of the motion is wrong, or both.