Another of the options you will be given is to change the spelling of the word to another word. This can also be done just this one time or for all the times it is found on the page. When it gives you this option it will also give you a list of similar words to choose from. You can then choose one of the words from the list or you can fix the word yourself.
If the word comes up as spelled wrong but you know it's right and you use the word often you can also choose to add the word to the spell checker's dictionary. This way you will never have that word come up in the spell checker ever again. If you don't see the word you want in the list you can click on the closest one or type a different spelling in and click on the suggest button. Then you will get more spellings to choose from.
If you only want to spell check one word you can highlight that word and click on it with your right mouse button. A menu will come up with alternate spellings for you to choose from. Just choose one and it's fixed.