she became a pillar of salt
"she became like a statue of salt" or "her body became like a tall stone of salt." Because she disobeyed the angel who told them not to look back at the city, God caused her to become something like a statue made out of rock salt.
The word "behold" draws attention to the surprising information that follows.
like the smoke of a furnace
This shows that it was a very large amount of smoke. AT: "like the smoke from a very large fire" (See: rc://en/ta/man/translate/figs-simile)