I have read through several threads answering this exact question. However these threads relate to older SharePoint editions and am unsure if my inability to implement the solution is due to version differences or more likely my own incompetence.
I am using SharePoint online via Office 365. I am having trouble adding a custom task list app to a subsite. It simply does not appear. The thread below answers this question, but I can't work out where to put the code in the answer given:
Any help would be much appreciated