Below the change box is a Show preview button. Pressing this will show you what your change will look like without saving your change (letting everybody see your changes.) You should always press this before you press Publish changes, which will let everybody see your change.
If you press Publish changes without pressing Show preview, everyone will see your change, even if it has a mistake. If you press show preview before, you can check if there are any mistakes. You can then go back to your change and fix the mistakes.