If one of the suggested words is correct, press the Down arrow or use the mouse to select the suggested word you'd like to use, and then press Return/Enter to apply it. If you make a mistake and choose the wrong word, simply undo the change (Edit > Undo) and then choose a different suggested word or edit the word using the Text tool.
If a word flagged as a typo is used only once (such as a person's name or location) and you know that it is spelled correctly, there is no need to fix it. The red underline you see in Design view is not displayed when you preview, publish, or export a site.
When working with commonly used words, such as business names or addresses, you can add the words to the Spell Checker dictionary so that they are not marked as typos.
Use the Text tool to right-click on a word you want to add to the dictionary, and then choose the Add to Dictionary option from the context menu that appears.
You can set the desired language (which in turn sets the Spell Checker language dictionary) for the entire site and for individual text frames.
To set the Spell Checker dictionary for the entire site, choose File > Site Properties. Click the Text tab, choose the desired language in the Language menu, and then click OK.