Learn Polish: Pan nie rozumie. - You do not understand, sir.

Pan is the formal way to say 'you' when speaking directly to a man you do not know well, like a customer, a stranger, or a professional. Ty is the informal 'you' used only for friends, family, and children.

If this means 'you do not understand', why doesn't the verb end in '-sz' like in rozumiesz?

When we use formal pronouns like Pan (sir) or Pani (madam), Polish requires us to use the 'he/she/it' (3rd person singular) form of the verb. So, instead of the informal ty rozumiesz (you understand), we say Pan rozumie (literally: 'the gentleman understands').

Could Pan nie rozumie also mean 'The man doesn't understand'?

Yes, it can! Out of context, Pan can mean 'the gentleman' or 'the man'. So this sentence could mean 'The man doesn't understand' when talking about someone else, or 'You don't understand, sir' when speaking directly to a man. Real-life context usually makes it obvious which one you mean.

Why is nie placed directly before the verb?

In Polish, the word for 'not' (nie) always goes immediately before the verb it is negating. Polish doesn't use helper words like 'do' or 'does' to make negatives, so you simply put nie right before rozumie.