Highlight the email by left clicking on it and hit the delete button. To do multiples at one time highlight one at the top of the page, scroll down to the bottom and hit shirt key and left click while holding the shift key. This will highlight all in between those two points. Then hit delete.
After that you need to go to the trash folder and delete them there or all you did was move them from one place to another. Usually you can just empty the trash to get rid of all of them at once.
