Most people are familiar with article writing.
Newspapers, magazines and many news and feature websites are packed with article writing.
An article can be about anything. This writing is an article. It talks about writing articles.
Articles are non-fiction. They can be news, such as a story about a City Council meeting. They can be a review of a product like a new washing machine. They can be an interview with someone.
An article has one topic – the City Council meeting; the washing machine; the person being interviewed. It should stay on that topic, but it can branch widely. An interview with a famous person could talk about his life, his work, his inspirations, family, future goals or anything interesting about that person. People who interview Jay Leno ask him about humor, cars and motorcycles as these are what he is famous for.
An article can have an opinion, but it has to be strongly supported.