Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
HI Fancine,
The red wavy lines are indicators of spelling errors. If you are getting errors and you are certain your spelling is correct, you probably have a different language from the one you want to use applied to the passage.
Select the underlined text, then go to the Tools menu and choose Language. It will display the language of the selected text. If the language isn't what you expected, select the language you want to use.
Keep in mind, language is like other text formatting like bold or italics. You select the text you want to set the language for and then choose the language from Language settings.