Voilà and Viola are easily confused words. One word is French, and been adopted into English.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It suggests what word you may want to save time, but quite often, its suggestions couldn’t be more off base and produces humorous results.
Voilà is an interjection. This a word used to express excited emotion. When a person says Voilà they are indicating they feel successful completion, even mastery: “Voilà! Check out my latest artwork!”
Viola is a noun. It means a large string instrument played with a bow. Violas are larger than violins and consequently have a lower sound range. It can also mean violet plants. [Some women are named Viola, and this is for the violet flower meaning.]
The following story uses both words correctly:
Vino spent months composing his viola concerto for the charity concert. When he was finally done, he performed it for his mom and her friends, finishing with “Voilà! What’d you think guys? Am I ready for the Viola Gardens Show?”