https://www.mobileread.com/forums/forumdisplay.php?f=236
would probably be a better place for dedicated help...
but since I hadn't run calibre in forever...
I connected my kindle... Device appears
I choose something I have imported that is not on the device and choose SEND TO DEVICE (its the second option on the "right click" list)
It sends to the device. I choose SHOW BOOKS IN MAIN MEMORY
it appears in the devices list of stuff with a green tick
I eject device.
Thats it.