Kickstart is already on a chip inside the Amiga 500, the Amiga that needed a kickstart is Amiga 1000 (Amiga 3000 too with kickstart 1.4, but that's pretty rare).
the Gotek can be purchase here:
https://amigastore.eu/323-usb-floppy...r-gotek.html#/ or any other amiga store, or Ebay. Look for the one that has flashflopppy installed. LCD option is highly recommended, so you can see the file names.
To install the Gotek, remove the floppy drive power cable and ribbon cable, install the Gotek, plug both cables back and you are almost ready to go.
For best results, watch some youtube videos, it's faster then writing.