Step 1: Click into your Parent Goal from your "You" page
Step 2: Select the Key result you would like to add a Key Result to
Step 3: Select Options and edit
Step 4: Edit your Key Result. Don't forget to hit Save!
Lastly, publish your Key result!
Note: The "Goal cycle", "Owner", "Type", and "Visibility" options in the key result are components of the cascading goals functionality. Click here to learn more about this feature.