You need to install the QTP for QC add-in.

Go to your Quality Center main page (the url should look like http://{Insert your ServerName here}/qcbin/)
On this page you should see a link that says 'Add-Ins Page'. Click that link.

Alternatively, if you are already logged in to QC, click Help and then click 'Add-ins Page' and the same page will display.

On the Add-Ins page, you should see a link that says 'More Quality Center Add-ins'. Click that link
On the next page, you should see a link that says 'QuickTest Professional Add-in'

At this point, depending on your system's set-up, you may be able to directly download the add-in from your QC server, or you may experience a login screen to the HP site. If so, you or someone you work with that has access to the HP site will have to log on and download the appropriate add-in.

Once the QTP for QC add-in is downloaded, just install it and you should be able to see the QTP scripts in the Test Script tab.

It isn't referring to a folder, but the main QC page url. Yours may also need a port number to access the main QC page as well, such as:

http://QCServerName:8080/qcbin

This will take you to the main QC welcome page in your browser, and you should see several links. You would select the Add-ins link that was mentioned above, and then select the More Addins link to find the QuickTest Professional addin. Make sure you select the correct download that matches your QTP version.

Install the QuickTest Professional Add-in. It can be found by going to your http://servername/qcbin/ folder, the go to Add-Ins, More Add Ins.