Articles are determiners that help show if a noun is general or specific.
Some common articles are a and an which are indefinite articles. They are used with a singular noun when that noun is non-specific.
In this example, Cara bought a car. But we don't have any further information to tell us about which car Cara bought. Thus, the noun is non-specific.
The is a definite article. The shows a specific reference point. It can be used with both plural and singular nouns, as well as both countable and uncountable nouns.
In this example, the word "the" indicates that the author is talking about a specific park.