the power store files need to go into the website root.
in most XAMPP installations the localhost/ web address maps to the c:\xampp\htdocs folder
if you have XAMP configured to use a different path for the localhost address, then use this other path.
additional, you may want the power store files to be in a subdirectory of your site:
if this is the case, then create a subdirectory for the power store files in the site htdocs folder.
see this page for details on enabling the Curl extension in XAMPP: