Here's a breakdown:
* Blue wavy line: This usually means the software has detected a possible spelling error.
* Red wavy line: This usually means the software has detected a possible grammar error.
It's important to note that the software's suggestions are not always perfect! You may need to review the highlighted text and make a judgment call based on your own understanding of the context.
If you're not sure what the problem is, you can right-click on the underlined word or phrase and see the suggested corrections.