How do I delete multiple messages in one rather than one by one

You'll want to become familiar with selection methods such as control+click, shift+click, and control-a (on a Macintosh, command+click, shift+click and command-a). The one that you probably want to use most in your inbox is control+click (command+click on Macintosh). After selecting, press <delete> or, to delete immediately instead of putting the messages in the trash folder, shift+delete.