Point me in right direction? Advice for my first project needed.

So, I've recently begun learning android, and am really falling in love with it. I have a yearish of programming experience but have never made something I could put in a portfolio. So for my first portfolio idea, I could use some advice on where to look/focus my time.

I essentially want to make an app that notifies a user of the distance between them and another user. So, basically an app where me & my friend can calculate the distance between each other. And both parties would have to grant permission to each other of course.

So, right off the bat I assume gps-location/coordinates would be needed, and perhaps setting up a server for both parties to send/receive the other's info? What other major android concepts would be NECESSARY to begin making this? And if possible which tools/concepts might make this idea easier for the user or easier to implement?

Thank you!!