Partners are external service providers who can be a part of your chosen product, e.g. a restaurant where you stop for lunch. Your partner will receive a notification when the experience you have linked them to is booked.
Here's more information on how to create a new partner if you haven't created your partner yet.
How do I add a partner to an experience?
Select the product from your list of experiences and scroll down to "Partner services". Select "Add" up in the right hand corner of the "Partner services" window.
Select the name of the partner from the drop-down list along with the additional information that's being requested.
Please note that you can choose between price per person or per booking. The price is only between the tour operator and the partner - the end customer will never see it.