I know the spelling is completely off and wrong but this is how i hear it. Short it is phonetic spelled - the way I'd would spell it in German.
My friends told me it is a polite was to say "co".
What does "sucham" exactly mean?
It is actually "słucham" and if spoken quickly and carelessly may sound like "sucham". The meaning is "I am listening" and, as your friends said, it is more polite way of saying "co?" (what?) whenever you want somebody to clarify or repeat something. Although it looks as though it were an affirmative sentence, you say it with a rising tone (like in questions).