When you're planning an activity, you have the option to make it a recurring task.
To set one up is simple! You simply select Plan Activity > Repeat > then select at which interval you would like it to repeat from the menu
After creating a repeating task, the future dated tasks will not appear in your planned activities until the current task has been marked as 'done' or 'won't do'.
The next planned activity is set from the latest task date, one interval forward. Some example scenarios:
Task is set to Apr 5, repeat interval set to monthly, I complete the task on Apr 8
Next task: May 5
Original recurring task set to Apr 5, repeat interval set to monthly, after a few months in August I change from Aug 5 to Aug 12 and complete
Next task: Sep 12
Note that it is the task date and not the logged note date which sets the date for the next task.
If you would like the planned activity to stop repeating after a while, just select "Don't repeat" on the most recently assigned task.