You use the when you have already mentioned the thing you are talking about.
For example:
| "She's got two children; a girl and a boy. The girl's eight and the boy's fourteen." |
We use the to talk about geographical points on the globe.
For example:
| the North Pole, the equator |
We use the to talk about rivers, oceans and seas
For example:
| the Nile, the Pacific, the English channel |
We also use the before certain nouns when we know there is only one of a particular thing.
For example:
| the rain, the sun, the wind, the world, the earth, the White House etc.. |
