A GOTEK drive is a floppy drive emulator. They are usually sold as drives for Yamaha keyboards/samplers, sewing machines etc. They also come with software for Windows.
It uses a USB drive to store floppy images.
With the GOTEK drive you no long need diskettes.
What the GOTEK drive is NOT: it's not a usb port where you can connect keyboard, mice or other usb peripherals.
With a simple operation of firmware upgrade you can flash the drive to be used for the Amiga.
After a firmware update, It can replace the internal floppydrive of your amiga, or be used in an external enclosure.
The drive can be aquired for around $20 on ebay including free shipping, and a programming cable costs around $2.
There are plenty of people selling pre-prgrammed drives, but they are usually atleast the double price, and the original Author of the fimware doesn't get any money of these sales, though he was the one spending a long time developing it. I don't recommend that you support the sellers who sell the pre-programmed GOTEK drives.
Below is a drive in an external enclosure.
You can flip through multiple adf files (disks) on the USB drive by pressing one of the 2 buttons.
You "program" a position for an adf file by booting on disk 000 on your Amiga, this position is the only position that cannot be changed. This is the Selector disk -selector.adf- which can be found in the firmware zip package.
The main author's blog site can be found on the link below, and the download link for the firmware package with the selector disk is located in the bottom of the blog post.