When ever you click on any folders icon, explorer.exe open. Click on any folder inside it and explorer.exe will open this folder also in the same process. This is so, by default, Explorer opens all folders within the same process.
Open Folder in New Process
However should you wish to open a particular folder in a different process you can do so easily. Simply press Shift key and right click on the folder you wish to open in a new process.
From the context menu option, click Open in New Process.
Explorer.exe will now open another instance, and the folder will be opened as a new process.
It is to be noted that Open in New Process is different from Open in New Window. In the latter case, two folders could be running in the same explorer.exe process. Opening a folder in a new process is useful, as if one instance of explorer.exe were to crash, the other process would still be up and running.
Useful if your Windows explorer crashes frequently and you need to troubleshoot.