not know one end (of something) from another

not know one end (of something) from another

To have absolutely no knowledge about something. I don't know one end from another when it comes to computers, so you'll have to explain this to me really slowly. What's an attachment again? Jeff wouldn't know one end of a baby from another. Thank goodness Frank is there to help babysit.
See also: another, end, know, not, one
Farlex Dictionary of Idioms.

not know/not be able to tell ˌone end of something from the ˈother

(informal) know absolutely nothing about something, for example a machine: Don’t ask me to fix the car. I don’t know one end of an engine from the other.
See also: able, end, know, not, of, one, other, something, tell
Farlex Partner Idioms Dictionary
See also:
  • bedsheets
  • be no question that (something will happen/is the case)
  • be certain that (something will happen or is the case)
  • where on God's green earth
  • look for (someone or something) high and low
  • look for high and low
  • (I'll be) hanged if I know!
  • by all means
  • you can bet the farm that (something will happen or is the case)
  • accepted