HuSi provides a Spell Checking facility. Should you wish to use it, press the 'Spellcheck' button instead of 'Preview'.
Any words that the spell checker doesn't recognise will be highlighted. Correct any mistakes as appropriate.
Different dictionaries, eg for American or British English, can be selected in your Display Preferences.
Be aware that sometimes the spellcheck can interfere with formatting. Although this is considered a bug, it does occur. You should always do a bare 'Preview' before posting, just to make sure the formatting is as you expect.