• Click the cogwheel icon in the top right of your inbox screen and go to Settings.
• Then click the tab at the top that says Forwarding and IMAP/POP
• At the top it has a button that says "Add forwarding address"
All email should then be sent to that email address. Keep in mind, all email is just forwarded. If you reply to a forwarded email, it will send from your secondary email address that it was forwarded to.