When you talk to or about someone you can use their name first and then afterwards use a pronoun. The problem with this is that it you can, without bad intentions, insult people or sound ignorant.
They and them
It is fine to talk about a group of people as ‘them’; just don’t complain about ‘them’ otherwise you shall sound ignorant, as in the following example.
“They come over here, imposing their culture on us. They take our jobs…
The easier option is to make sure you are not making general statements about huge groups of people.
He, she or they
Times have changed and it is not always obvious whether somebody is male or female. You might guess, but would you or the person you are talking about be embarrassed or feel awkward afterward? If you are in such a situation you might use ‘they’.
But Marc, ‘they’ is for groups.
Yes, it is, but it can also refer to individual people.
My sister’s new flatmate is called George. I don’t know if they’re a man or a woman because she hasn’t met them yet.
I hope this is helpful.