In order to receive coins from any other address you should provide your public address to the sender. To do so, you need to tap the “receive” button.

 

There, you will see a QR code which you can show to the sender as long as they have a QR scanner. Otherwise, you can copy the address by tapping on it. You can also tap “share” to send your public address via other applications such as “Mail”, “WhatsApp”, and others.