Use the possessive apostrophe when ownership is denoted. It is acceptable to use the apostrophe in contractions such as it's (for it is) and don't (for do not). The apostrophe is never used to form a plural noun.
- the lecturer's office (singular)
- the lecturers' timetables (plural)
- Christmas is just around the corner; it's just three days from today.
- The basket's were filled with apples and oranges.
According to the NZ Geographic Board, Hawke's Bay and Arthur's Pass are the only two names which have a possessive apostrophe.