Data share between above two parties is possible via 3 different ways:
Audience Marketplace : When both parties have AAM and Audience Marketplace contract included. (You can reach out to CSM to get this provisioned)
2nd Party Data share: When both parties have AAM, a destination in sender's account will be created by Customer Care which will send data into receiver's S3/FTP bucket. Here datasource of sender and FTP/S3 bucket of receiver will be required.
File Onboarding : This can be done when sender has no AAM account. Sender has to format files in accordance with given documentation and upload file into receiver's S3/FTP bucket from where AAM will pick and process the files.