Configure here what should WinCatalog do if you perform a double click on the item. There are 3 options are available:
Show properties - WinCatalog will open Item Properties Dialog if you double click on an item.
Open in associated application - WinCatalog will try to open file in the associated application. This option is available for files only. Double click on folder will navigate inside the folder. Double click on non-file item will open it's properties.
Open in Explorer - WinCatalog will try to run Windows Explorer and navigate the physical folder which contain the file. This option is available for files and folders. Double click on non-file item will open it's properties.