The Internet is a dangerous place, seemingly moreso today than it has ever been. Sensible precautions such as Anti-Virus, care with respect to the links you click and caution with email attachments, can make your experience a safer and more enjoyable one. Backups can help, allowing you a degree of surety in recovering your data in the event of a problem with your computer.
No matter how easy they appear to be to use, bear in mind that ALL operating systems are (without exception) highly complex designed largely by humans. From that fact alone you can draw some provisional conclusions.
Passwords are one of the most important ways to protect your computer system yet most computer users get it wrong in several key respects. It is generally considered a bad idea to use the same password across multiple systems while it is usually considered a good idea to use a strong password.