As you type, Word will warn you if make spelling or grammar mistakes by inserting a wavy red, green, or blue underline beneath the text that it thinks is an error, as follows:
Red underline This indicates either a possible spelling error or that Word doesn't recognize a word, such as a proper name or place.
Green underline Word thinks that grammar should be revised.
Blue underline A word is spelled correctly but does not seem to be the correct word for the sentence. For example, you type "too," but the word should be "to."
What do you do about the underlines? You right-click an underlined word to see suggested revisions (every once in a while Word may not have any alternate spellings). Click a revision to replace the word in the document and get rid of the underlines. Note that if you print a document with these underlines, they will not show up on printed pages.
A note of caution about green and blue underlines: Word is really good at spelling, which is pretty straightforward, most of the time. But grammar and correct word usage take some judgment. If you think that you are right, and Word is wrong, you can ignore the suggested revisions and get rid of the underlines. You'll see how in the practice.
Tip If you prefer not to stop every time you see wavy underlines, you can just ignore them as you go. When you are through, you can tell Word to check spelling and grammar all at one time. You'll learn how in the practice.