If you’re composing in Rich Text – i.e., if you see the row of buttons along the top of the Compose window for Bold, Italics, etc., then click the button toward the left with a check-mark and “abc” on it. If you’re in Plain Text, click Spell Check at the top – it’s between Save As A Draft and Cancel.

If Spell Checker sees a misspelled word in your email message, a “Suggestions:” box opens on the upper right, with a few words it thinks you might be trying to spell. If one of Spell Checker’s suggestions is correct, click on it to select it, and then click Change. Click the down-arrow on the right end of Change to reveal “Change all occurrences” if you think you’ve misspelled the word throughout your email. They’ll all get fixed!