In business situations, or when talking to older generations, you will usually refer to them as "Mr X" "Mrs X" and so on. An un married woman is traditionally called "Miss X" and a married woman is traditionally called "Mrs X" and will change her surname to her husband's, although she does not have to. Often now, adult women are simply referred to as "Ms X", and it is only children who are called "Miss" although this can vary. In informal situations, amongst friends and family and often at work when talking to equals, you will call each other by your first name.
I hope that helps!