Share 'Il s'agissait de'

I find the use of s'agir quite tantalising. I think I know what it means, but not well enough to use it myself. It seems to be a mix of "it is/it includes/it involves/it consists of...".  The phrase that started me off was: Il s'agissait de trois pièces ... (describing a building layout).  Would the man in the street use this construction? It is used more in the written word than spoken? Are ther…