First of all you need to find and download the program you want to install. When the download process is complete you need to copy the CAB file and paste it somewhere on your device, I personally recommend to do this at the Storage Card. Note that some applications are zipped so you need to unarchive them to have the CAB file.
Now you need to open Window Mobile Phone File Explorer, located inside Start - Programs - File Explorer. Browse to the Storage Card or the location you used to copy the CAB file to. When you select and run it, a windows will appear, which asks you to Choose a location to install the program. It can be your Device or the Storage Card or My Storage, so select your choice and click below on Install. The process after that is fully automated and after the installation is complete it will show you confirmation screen.
You have completed installing the CAB file and you will be able to find the program in your Omnia now. Go to Start - programs and you will be able to find the application that you have install inside it.
