MakeUseOf posted 8 Ways To Spell & Grammar Check In Microsoft Word Using Different Dictionaries & Languages A quote from the article:

Microsoft Words built-in spelling and grammar checking tools work automatically most of the time, but there are many ways to customize them. You can even use AutoCorrect to speed up your typing. We used Word 2013 for this article. The interface should be fairly similar on Word 2010, too. In-line Spell Checking By default, Word will use in-line spell checking. Words you misspell will appear with a red squiggly underline just right-click the word you meant to type to correct each typo. Of course, Word doesnt know every word that exists especially names of things.

 8 Ways To Spell & Grammar Check In Microsoft Word Using Different Dictionaries & Languages @ MakeUseOf