Before you read further it may seem difficult to create a home-grown solution to send email results back to Sales Cloud because the Marketing Cloud Connector is supposed to serve this purpose. It sends individual email results back to Sales Cloud and they are associated with each contact. I think that might actually suit your needs better than trying to create something from scratch. If you know this option won't work for you, read on:
Are you looking to query general data views in Marketing Cloud? They're organized as follows:
_Job: A Job is an email that takes place in a specific point in time. When you hit "Send" or schedule an email, a Job is created.
_Sent: Every email that a job sends gets logged here as an item in _Sent.
_Open: Every time a tracked email is opened it gets logged here.
My guess is that if you're looking to write a query to look for open data from a specific email campaign, you'd want to look in the _Open data extension for emails that match a specific date or job.