If a Canvas quiz is using the Proctorio monitoring option, students must use the Google Chrome browser with the Proctorio extension, on a computer, not a smartphone or tablet. If you haven't set up your computer properly, when you click the quiz, you'll get a screen like this:

Students need to click inside the orange error window where it says "click here", but if you click Take the Quiz, you'll get a screen asking for an Access Code, like this:

The solution to the Access Code problem is to go back to the quiz, and click the Extension link. Use Chrome. Install the Proctorio extension. Enable the Proctorio extension for incognito mode. The quiz walks the student through these things.