Which Formulas to use in Excel

Hello all

I am trying to create quizzes for work, similar to the type that I see on the internet. Can anyone tell me which formula to use to return the value of either correct or incorrect in a spreadsheet, for example if i ask the question which operating system are you using, i would want my student to say XP, i then want the spreadsheet to check the contents of the cell and return a value of either incorrect or correct depending on what the student entered. i have been all around the formula help screens and the wizard with no joy. thank you