Go to the "Goals & OKRs" section in the menu. 
Then create or choose the goal you want to edit. Go down to the line "Tasks".
In order to add a task click on" + " sign.

You can write specific tasks within the skill, you also have an opportunity to frame tasks into the checklist. Add materials that will be needed for an employee. You can add them from knowledge base, recommended materials or upload it from the computer.