There are two ways to create task templates.
One way is be going to "Templates" on the lefthand side and clicking on "+ Add New". You will name your template. Then you can start adding monthly tasks on the right hand side.
The second way is directly inside of a campaign overview itself. You can add tasks and then click the gear icon above the tasks. That will bring a drop down option that says "Save as Template".
The gear icon is also where you would "Load from Template" if you have an existing template you would like to use.
For more information on creating task templates, watch this video.
For more information on updating/editing task templates, you can watch this video.