I’m afraid I don’t really understand this part, The SD card is the operating system of the Raspberry Pi based emonBase. without it you cannot get anything to work at all, not emoncms nor wifi So to do those things you must have an SD card inserted, perhaps the option you selected was for a complete emonBase including SDcard and the shop put it in place for you? It is a microSD card and it fits in the microSD card slot on the underside of the Pi at the opposite end to the Ethernet and USB ports.
I thought I hadn’t bought the SD Card, but after posting, I found that I had.
It is pretty small ! I didn’t see it there.
Sorry for the noob question. Good to know the forums are a source for help !