There are four broad categories of fake news, according to media professor Melissa Zimdars of Merrimack College.
No single topic falls under a single category - for example, false or misleading medical news may be entirely fabricated (Category 1), may intentionally misinterpret facts or misrepresent data (Category 2), may be accurate or partially accurate but use an alarmist title to get your attention (Category 3) or may be a critique on modern medical practice (Category 4.) Some articles fall under more than one category. It is up to you to do the legwork to make sure your information is good.
Fake news would not be a problem if people knew it when they saw it. It matters because most people have trouble identifying fake news.
A Pew Research study (link below) showed that 64% of Americans had a great deal of confusion with an additional 24% having some confusion. That's a lot!
Why Should You Care About Whether Or Not Your News Is Real or Fake?