they
The German word 'sie' is the plural form of 'er' (he) and 'sie' (she), and is used to refer to a group of people or things. It can also be used as a formal way to address someone, similar to the English 'you'. It is important to note that 'sie' is also the formal way to say 'she' in German, but in this context, it is used to mean 'they'.
She has an apple
In this context, 'Sie' refers to 'she'. This sentence is using the verb 'hat' which is the third person singular form of 'haben' (to have) in present tense. It's talking about a female who has an apple.
Do you know him?
Here, 'Sie' is being used in the formal way to address someone as 'you,' which is typical in formal, business, or respectful situations. The sentence is using the verb 'kennen' which means 'to know' and is asking whether the person being addressed knows him.
They are waiting for the bus
In this instance, 'Sie' is referring to 'they.' The sentence is in the present tense, using the verb 'warten' which means 'to wait,' implying that there is a group of people waiting for the bus.