If you have a connected Gmail, Exchange, or Office 365 account, and add a new contact in your email, they will be added as a contact in Engage as well, but it may not happen immediately. Our software communicates with your email, but has to do a "refresh" to pull in the new information (email history, new contacts). That refresh happens each night automatically, but can also be done manually by going to Connected Accounts under Settings and selecting Sync (see screenshot below).
Keep in mind that Outlook also has to communicate with your email server and has to refresh its information regularly as well (i.e. Refer.com <------syncs to-----> email@example.com <------syncs to-------> Outlook).
*Options to sync with Exchange and Office 365 are only available for Enterprise accounts.