How do I delete junk mail

You can select all the junk mail and delete them at one time or you can delete them one at a time. If your junk mail is in your Junk Mail folder in Mail, then select one message and press COMMAND-A to select all messages. CTRL- or RIGHT-click on the selection and choose Delete from the context menu or click on the Trashcan button in Mail's toolbar.

If you wish to set up an automatic removal, then open Mail's preferences. Click on the Accounts button in the toolbar. Select your email account from the left side list, then click on the Mailbox Behaviors tab button. You will see options for handling junk mail and trash. Select the settings you prefer.

The same way you delete an email message.