To deploy software, create a new GPO object (one that applies to Users or Computers)
Edit the new GPO.
Goto: "Computer Configuration" -> "Policies" -> "Software Settings"
Right Click "Software Installation" Click: New -> "Package"
Select the MSI you want to deploy.
Choose the deployment type, Addigned for Computer Deployments, Published for User Deployments.
Assigned is basically a forced install. Published allows the user to interact with the install and optionally allow user removal of the package.
NOTE:
Make sure the path to the MSI is accessible to the Computer or User which will the Deployment applies. As an example, for computer deployments, make sure Domain Computers have read access tot he MSI. For users make sure Domain Users (Or your targed group/user) has read access to the MSI.
Troublshooting
You can enable Software Installation logging on the target PC. To do this open 'regedit' Goto: HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ Create a new KEY named 'Diagnostics' within Diagnostics\ create a DWord named 'AppMgmtDebugLevel' with a Hex value of '4b' or decimal value of 75.
This will enable Verbose Logging of Software Deployments. The log is stored in %windir%\Debug\UserMode\appmgmt.log