Symphony.

My site will encourage multiple user with author account to submit their own articles for pending until the editor will approve for public consume. I have no idea what is the best way for editor to "approve" it?

The simplest way is to use a checkbox or a select box to retain state (pending/approved/rejected). Perhaps you'd like to try the Status Field which is a select box that remembered previous values, providing an audit trail of status changes.

You could write a custom extension such that any time an article is created with a status of "pending", all editors get an email.

You could also use Publish Filtering, Backend Views or a Dashboard panel to present a list of pending articles to approvers.

You could also possibly use email-template manager (ETM) I think to send emails, but more or less its what Nick suggests.