Open OST Viewer software (For that, go to Start » Programs » OST Viewer - Viewing OST files, click the 'Add File' button present on the toolbar of OST Viewer software as shown underneath:
Click Browse button to select OST file from local drive and select one scan mode for loading OST file as shown in the below screenshot:
OST file will be loaded and you can view its contents easily as shown in the below screenshot:
Now, you can also switch the view from Horizontal View to Vertical View: