Mac OS is not impervious to problems. Granted it has less problems than Windows or Linux, it does suffer from some issues. So when it's time for a redo, here's how to do it:
1. Restart the computer
2. Press command and the letter R at the same time until you see the Apple logo
3. Click the wifi symbol in the top right corner and connect to a network.
4. Click on Reinstall Mac OS
5. Enter your Apple ID and password
6. Follow the instructions on the screen
Please note: No person or company paid me to say anything about any of the topics above. These are my opinions and what I have observed using the program personally. Your experience may vary. I am not responsible for any data loss that may occur. Use my guides at your own risk.