We use 'a' when we are refering to a type of thing or person, but don't know which one for certain. We use 'the' when we know to what we are refering. "Fred, what's new?" "Hi Tom. We bought a dog." ['a' dog, because we don't know which one up to this point. It could be any dog.] "What kind is the dog?" ['the' dog, because now we know which dog we are refering to - the dog that Fred bought."] "The dog is a poodle." ['the' dog, because we still know which dog we are talking about.] If Fred and Tom had talked about buying a particular dog earlier and Tom knew that Fred was going to buy a particular dog - the poodle in this case - the sentence might have been: "Hi Fred. Did you buy the dog you were talking about. The poodle?" [Again, we use 'the' because we know definitely which dog." "Do you own a dog?" = "Do you own any dog?" [We don't know which dog - we are trying to find out.]

I agree with the above comments, and will just add this: Articles are something that you cannot ignore. You will need to learn them properly. Omitting them is not an option. Our nouns need a-nailin' down! :)

We call them "Articals" "the" for specific or particular nouns "a/an" for non-specific or non-particular nouns and "a/an" the indefinite article and "the" for the definite article . example: when I say "Let's play the game" I mean a specific game . If I say, "Let's play a game" I mean any game. "A/An" are always singular. "The" is singular or plural. ps: Some plural nouns don't use an article. so when using articles, it's important to also know the difference between count and noncount nouns.

''the'' and ''a'' are two articles