How do I keep a GPS enabled app in memory on iOS?

I have been searching for the option in XCode, but none seems to work. WhatI want to do is pull GPS coordinates every 2 seconds, and create a path the user took. I also want a timer running, so I can calculate speed. It works very well when the app is open, but when I press home, I dont see the blue bar appear, and it doesnt stay open in background. Please, help. the project is due in a few days

thank yo for your assistance