An article marks a noun to indicate its definiteness.
In English, we use articles to specify the definiteness of the noun, but Mandarin Chinese works differently.
In Chinese, there is 这 (zhè), which is used as a definite article ("the") and 一个 (Yīgè) for indefinite articles.
The house of your aunt is old.
Gūgū de zhè fángzi shì jiù de.
The math book is very big.
Běn zhè shùxué shū shì fēicháng dà de.
He bought a wallet.
Tā mǎi le yīgè gè qiánbāo.
I bring an apple.
Wǒ dài yīgè gè píngguǒ.
You can give some candies.
Nǐ kěyǐ gěi yīgè xiē tángguǒ.
Key points to remember
Definite Articles: Chinese language doesn’t have the exactly word "the" at all. If one wants to say "the apple" in Chinese: 这蘋果的, one is really saying: "this apple/that apple/those apples/these apples".
Indefinite Articles: There are the indefinite articles: “A”, “An” and “Some” in English language, but if one wants to say "a dish" (一个盤), one is really saying "one dish" (一盤).