Introduction
In the "Mail" application, click Mail, and click Preferences. Then, click Junk Mail and check the box for Enable junk mail filtering.
Instructions
1) Open the Mail application.
2) In your Mac's menu bar, click Mail. Then, choose Preferences.
3) Under the Junk Mail tab, check the box next to "Enable junk mail filtering". Finally, choose your desired settings.
OUTCOME
The Mail app on your Mac will filter junk email.