There are a lot of rules for articles:
1. Don't put an article in front of the name of a place.
Correct: Minneapolis is a great city.
is a great city.
But it's correct to use the name of a place as an adjective:
The Minneapolis skyline is
beautiful at night.
2. Indefinite amounts or general
qualities don't take an article.
Pennies are made of copper.
in this penny is turning brown. (this is a specific amount)
Water is good for you.
in this glass tastes bad. (this is
a specific amount)
3. Don't use an article with possessive nouns
the Paul's website.