When we refer to the negative article in German, we mean using "kein" to negate a noun.
The lesson on negation tells you when to use "kein."
"Kein" is declined like / has the same endings as possessive determiners.
When do you use der, die, and das? Everything about the topic of gender can be found here: Articles and Gender.
Guess articles right 75% of the time even when you haven't memorized it yet! Article Trick.
When do you use der / die / das, and when ein / eine? ⇒ Definite and Indefinite Articles
Sometimes we don't use any article: The Zero Article.
Using an article to negate a noun: „Kein“.