By default the emails are listed in Classic view and the emails open in the Vertical Preview pane. You can customize the behavior to suit your preferences from the Settings. The 'Classic' layout for email listing is spacious with ample spcing beween each email. However, to view more emails per page, you can switch to 'Compact' view, which reduces the white space and provides you more emails to view in the listing.
In the Vertical Three pane View, you can quickly navigate between emails and read them at ease. The different icons along with the menu drop down help you to perform the common actions in the email. To Reply, Reply All or Forward, use the icons near the drop down menu. For specific actions on the particular email, you can use the menu options in the drop down. For generic actions like delete, move to folder and so on, use the icons and actions in the Top bar.