Hi,
The parent category is the category where vendor categories would be created.
You have to use the option "Change vendor root category" to set the default root for vendors.
The value "Vendor home" would set the vendor category as the root.
The value "Yes" would allow you to set a specific root with the option "Vendors default root category" (in HikaMarket configuration for the default root but this value could be override for each vendors).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.