There are many ways to learn to code these days. From coding bootcamps like Flatiron School to online courses to totally free beginner resources. The best way to learn to code depends on many factors, but the most important one is you. See what course is best for you.
Maybe you can try pasting your string in there? There's no submit button, it's not being saved anywhere, just being processed in your browser. Just 'tab' out of any input field after changing it to see the new values in the output fields.