Hi Jayasree,
For Login function you can use signin javascript action comes in nanoflow commons by passing username and password.
If it returns 200 the sign is success else it is failed.
Hi Jayasree,
This functionality is already build in once you create a new app with the 'Blank Native Mobile App' template, so I would suggest creating a new app with that template so you can inspect the functionality within that new app and use that logic within your own app.
Good luck!