The "Captcha" is used to check if you're an actual living human being, and not a hacking robot trying to hack all our system secrets.
If the "Captcha" presents you with the image of a number, you simple enter the number as you see it. Numbers are presented if hacking robots are quiet, and risk is low.
If you see two WORDS, hacking robots are active and you have to work a little harder. When two words are presented, one word is clear and readable. The OTHER word is twisted and jumbled. The twisted word appears to be impossible, but all that's required is your best human-powered GUESS at what the letters are. Your guess doesn't have to be 100% exact, just a reasonable human guess. Type BOTH words (the readable word and your best guess at the jumbled word) in the box.