Your venue is asking to be added (named) as an Additional Insured because if you or any of your guests cause any damage to the venue or an injury at the event, the venue wants to be able to make a claim directly on your insurance policy. This does not cost you anything and allows the venue to go after your insurance company vs. you for damages or injuries. You can name your venue and the venue owners or managers as Additional Insureds. Vendors cannot be named as an Additional Insured.