The means something like 'you know which one I mean'. It is used with uncountable, singular and plural nouns.
the water (uncountable) the table (singular countable) the stars (plural countable)
We use the: a. to talk about people and things that we have already mentioned. She's got two children: a girl and a boy. The boy s fourteen and the girl's eight. b. when we are saying which people or things we mean.
Who's the girl in the car over there with John?
c. when it is clear from the situation which people or things we mean.
Could you close the door? (Only one door is open.) 'Where's Ann?' 'In the kitchen.' Could you pass the salt?
We do not use the with other determiners (for example my, this, some.)
This is my uncle. (NOT . . . the my uncle.) I like this beer. (NOT . . . the this beer.)
We do not usually use the with proper names (there are some exceptions . Mary lives in Switzerland. (NOT The Mary lives in the-Switzerland) We do not usually use the to talk about things in general — the does not mean 'all'. Books are expensive. (NOT The books are expensive.)