its an NGO how do I go about creating or customizing the income stream line to reflect subscriptions
See http://guides.manager.io/businesses/settings/chart-of-accounts. Admittedly, detailed instructions are lacking. But under Settings >> Chart of Accounts, you can add, delete, and rename accounts. You can group them, assign code numbers (which control presentation order), and insert totals. Most of the discussion on this recently expanded capability has been in this forum. Search on the topic and read the threads.
My advice is to design your desired chart of accounts with your accountant prior to beginning. If you know what you need, Manager can almost certainly accommodate that.