Thunderbolt Port

I have never used the Thunderbolt Port at all.

I want to use it for to connect an external hard drive to it because I am just using the USB Ports.

It`s a Mac Mini late 2014 Mac OS Sierra Version 10.12.6 16GB Ram.

It looks like I have 2 Thunderbolt ports.

First I think I must have to have a Thunderbolt cable but the external hard drives have only a USB cable so can anybody help me with this issue.

Thanks