office web app had installed on our SharePoint server but we do not have word viewing and powerpoint service in central admin - services on server what can we do i need to config word viewing
You are mixing a few things.
Having office web apps installed, configured and connected to your farm is sufficent enough to view and edit office documents in the browser. You dont need to configure additional sharepoint components like to word- or powerpoint service.
Please check first if your configuration is working: http://[your office web apps/hosting/discovery
Check if you have completed all steps:
On the office web apps server
New-OfficeWebAppsFarm -InternalURL "http://servername" -AllowHttp -EditingEnabled
On the sharepoint server
New-SPWOPIBinding -ServerName -AllowHTTP
Office Web Apps - https://technet.microsoft.com/en-us/library/jj219455.aspx