In Unibox all emails are grouped by sender, meaning that the inbox overview consists of people instead of emails and that each sender appears only once.
Swipe actions on a sender are applied to all emails of that sender in the currently selected folders. (You can delete all emails from one sender with a single swipe from left to right.)
To perform actions on a single email only you can swipe the entire body of that email. Swiping from left to right allows you to delete or moving to spam (or archive if Inbox-Zero mode is enabled). Swiping from right to left opens a menu that allows you to e.g. star/flag, forward or move an email.
You can configure all actions from the menu as their own swipe actions in the settings. The swipes can be configured separately for sender and message actions.