हाय, evansircar! 'निश्चित लेख है. वह एक निश्चित संज्ञा प्रयोग किया जाता है.

I think that the rules about "the" could fill a book. But -- generally speaking -- you use "the" when you are referring to someone / something that was mentioned before. A specific person or thing. Tom: I need A pencil. Mona: Here you are. Tom: Thank you very much for THE pencil. ***** Sometimes we do not need to mention anyone first. Tom: I am very upset. Mona: Why? Tom: I took a taxi to work this morning, and THE driver drove very dangerously! (Although the driver was NOT mentioned earlier, we use "the" because we know that a taxicab has only ONE driver. So he (or "she") must be THE driver.) ***** This is a true story: One day I was walking down the street in my American city. I passed a store. The store was owned by people who did not speak English very well. They had this sign near the door: "If you want to enter this store, ring A bell." Of course, they should have written:" Ring THE bell." (That is, THE bell next to the door. But their sign said "Ring A bell." That meant that I could ring any bell that I wanted to ring!!!)

'The' is a determiner and precedes a noun.

we use The to refer to organizations such as( The police ).(The army) we use The to refer to people belonging to nation example (the Dutch)(The Irish).

You can check out my article about articles at http://chromatic-english.blogspot.jp/2013/01/articles-friend-of-foe-part-1.html I write about a friend who misuses 'the' in a sentence and some ways to determine when to use 'the' or 'a' in a sentence.