How do I connect incoming emails to contacts?

Your emails start syncing with the associated contact record once you have connected your emails either by forwarding your emails using the Bcc Email address or configuring Full Email Sync.

Each email is available to you on the records timeline and under the related tab and timeline in the side / quick view of the record. This keeps you up to date on your communication with the contact.

Not just associating your emails to the contacts. You can choose to associate your emails with the deals either automatically or manually.