Sir
The word 'señor' is a Spanish noun primarily used as a respectful term to address a man. In English, it translates to 'sir'. The term is widely used in formal or business situations, ideal for when refering to someone older or in a superior position. It is also the equivalent of 'Mr.' when used preceding a person's surname. For example, 'Señor Perez' would translate to 'Mr. Perez' in English.
Mr. Pérez is very kind.
This sentence introduces a man named Pérez and describes him as kind, using 'señor' to show respect.
That gentleman is waiting for the bus.
In this sentence, 'señor' refers to an unspecified man who is currently waiting for public transportation.
The man on the corner sells fruits.
Here, 'señor' describes a man who operates a fruit-selling business at a street corner.