what steps do i take to use a sd card for more space in macbook air

Hi, check if below link answers your question.

https://support.apple.com/en-in/HT204384

Given the fact two of my macs have these card-slots,

they've never been used. I've early Panasonic Lumix

DMC-FZ1, uses version of the card; that's mostly OK.

Card-slot on Mac mini in back, has been determent

to use of this technology; w/ too many wires there.

Seldom use the MacBook Pro, with similar card-slot.

You could simply use the SD card for 'drag n drop', or

other transfer, just like saving files in any other media.

..Some Mac users 'cloned' smaller systems on a Card..

There is not even a step. I or anyone else on here wouldn't recommend such a thing. However, you may consider expanding the SSD if it is possible, if not, then external hard drive.