There are few rules to use "The"
- when we are thinking of one particular thing
- Tom sat down on the chair nearest the door.
- when it is clear in the situation which thing or person we mean.
For example:
- In a room we talk about the light, the floor, the ceiling
- when there is only one of something
For example:
- What is the longest river in the world?
- we say: the sky, the sea, the ground, the country, the environment.
- (go to) the cinema, the theatre
- the radio, but television is without the.
- we use the before same (the same)




