To send or request lives, you need to tap on the lives icon in the top right-hand corner of the screen.
The maximum number of lives is 5. All lives over the maximum number will be stored in the inbox tab in the main menu of the game. When you need them, you can collect them from that tab and add them to your current lives.
Lives in the inbox tab are stored for a maximum of 1 month. Therefore, lives that you received from friends or society members more than a month ago will disappear over time.