'They' can also be used for the singular third person if the gender of the person is unknown, or to purposely be ambiguous, or neither male nor female. Some people choose to use 'they' as their pronouns. Singular 'they' is conjugated the same way as the plural form, similar to the matching conjugations of the plural and singular 'you' in English. Singular 'they' is never used for objects, only people.
'They' can also be used to refer to a generic group of people, such as "In Britain, they celebrate Christmas in December".