Sub-Goals can be added and managed from the goals page.
If a goal is listed as OPEN, then the button to Add/Update Sub-Goals will appear.
Clicking the button will bring up a separate box. Within this you can add new goals and update existing goals. You can't delete a sub-goal, instead you would mark it 'not achieved'.
If you fill all 5 rows, click Add/Update again and 5 more will appear.
If marking a sub-goal complete as 'achieved' or 'partially achieved' you can also add the completion date. Leaving this blank will default it to the day of update.
Once sub-goals are added, you'll see them on the full goals page with a progress meter.