If your Office Web APps installation is already done, you "just" need to configure SHarePoint 2013 to use the Web App Farm. There is a pretty good article on Technet about this (as most of the times these days):
http://technet.microsoft.com/en-us/library/ff431687.aspx
As you are in production you will need/want to run on HTTPS. The command is as simple as this:
New-SPWOPIBinding -ServerName <WacServerName>
#<WacServerName> is just the url without the schema for example; wac.mycompany.local and not https://wac.mycompany.local
Check out this document for additional configuration scenarios if you not already used it for your WAC setup:
http://technet.microsoft.com/en-us/library/jj219455.aspx