Applying for Italy visa from Karachi with spouse abroad as the sponsor

Can someone tell the process to apply for Italy visa from Karachi for a person who will have their trip sponsored by their spouse? Like after filling the online form here in Karachi, even if one gets the appointment then can they just get themselves with the documents or do they need their spouse to go as well as he will be the sponsor?

Anyone who has a similar experience and can share the steps involved, kindly share it