How to add an application server role to your SharePoint farm

To add an application sever with an application server role to your SharePoint farm run this PowerShell commands:

Connect-SPConfigurationDatabase -DatabaseServer "MySqlServer" -DatabaseName "MySharePointFarmName_SharePoint_Config" -Passphrase "myPassPhrase"
Install-SPHelpCollection -All
Initialize-SPResourceSecurity
Install-SPService
Install-SPFeature -AllExistingFeatures
Install-SPApplicationContent

For more infomation on this read this technet article “Add a Web or application server to the farm (SharePoint Server 2010)” - http://technet.microsoft.com/en-us/library/cc261752.aspx