"Can you tell me how to find out if my drive is USB3, and how I can download the software onto it?"
The external drive MUST be an SSD.
You can't get "better speeds" from a platter-based hard drive.
You can either buy an SSD that is "pre-assembled" (such as a Samsung t5 or t7)
or...
You can buy a 2.5" SATA SSD and a USB3 2.5" enclosure, and "do it yourself".
You didn't tell us
what capacity your internal drive is.
Is it 1tb?
500gb?
Something else?
You can find this out with the "system information" app in the utilities folder.
If it's 1tb or 500gb, get an SSD that's the same size.
Use disk utility to erase/initialize it to APFS, GUID partition format.
Then, download CarbonCopyCloner from here:
www.bombich.com
CCC is FREE to download and use for 30 days, this will cost you nothing.
Next, use CCC to "clone" the contents of the internal drive to the external SSD.
CCC can even clone the recovery partition for you.
It's one of the best pieces of Mac software out there.
When done, go to the startup disk preference pane and set the SSD to be "the new boot drive".
Then reboot.
You should now be booting from the SSD.
Because SSD's run MUCH faster than a platter-based drive (particularly a 5400rpm drive that may be inside the 2014 Mini), booting and running will go considerably faster.