Word 2013 has an internal library stocked with zillions of words, all spelled correctly. Every time you type a word, it’s checked against that dictionary. When the word isn’t found, it’s marked as suspect in your document. The mark is a red zigzag underline.
My advice: Keep typing. Don’t let the “red zigzag of a failed elementary education” perturb you. Focus on getting your thoughts up on the screen rather than on stopping and fussing over inevitable typos.
When you’re ready, say, during one of those inevitable pauses that takes place as you write, go back and fix your spelling errors. Here's what to do:
Locate the misspelled word.
Look for the red zigzag underline.
Right-click the misspelled word.
Up pops a shortcut menu.
Choose from the list the word you intended to type.
The word fancy fits the bill. Click that word and it’s automatically inserted into your document, to replace the spurious word.
If the word you intended to type isn’t on the list, don’t fret. You may have to use a traditional dictionary (the paper kind) or take another stab at spelling the word phonetically and then correct it again.
When the word is spelled correctly and Word is just too stupid to recognize it, you can add the word to its dictionary.
Word turns off automatic proofing when your document grows larger than a specific size. For example, when the document is more than 100 pages long, automatic spell-checking is disabled. A warning appears, to alert you when this happens. Note that you can still manually spell-check.
Just because your document appears to contain no errors doesn't mean that everything is perfect. You have no better way to proof a document than to read it with human eyes.