But the flash drive has a built in USB-C port as well as a regular USB. I can plug the flash drive directly into my phone. I still need this OTG cable? Also, what is an OTG cable?You need an OTG cable between the phone's USB port and the drive. (There are short ones available on eBay from China for about 99 cents, shipping included. They work as well as the $40 ones from name-brand manufacturers. I've been using one for over a year.)
But the flash drive has a built in USB-C port as well as a regular USB. I can plug the flash drive directly into my phone. I still need this OTG cable? Also, what is an OTG cable?
OTG means on-the-go. You shouldn't need an adapter if it already has a USB-C port. Do you have OTG enabled in storage settings?