If the spell checker found any questionable words, it will display them as drop-down boxes, with alternate suggested spellings available. Select the desired spelling from the drop-down box, so it is displayed. Whatever spelling is selected when you click on one of the Make Changes buttons is the spelling that will appear in the final copy. If the desired spelling is not listed, then you can use the Make Changes and Return to Editor button to change it manually.
Proofreading
Whether or not the spell checker identified any misspellings, you should still proofread your message. The spell checker does not check for grammar, nor can it check for typos that result in a word that is in the dictionary, but not the one you wanted.
About Word Wrapping
The word wrapping you see here is not the same as the word wrapping your message will have when saved -- for a more accurate idea of how your message will be wrapped, use the Make Changes and Return to Editor button.