I do not have an icon to send or receive lives. Friends have sent lives but I am not able to get them as there no place to get them.
Gail, when you need lives you'll see a + on the lives heart (top left in the game), click it to ask for lives.
When your friends send messages asking for lives the 'message owl' will bring them, you'll see him bottom right in the game.
Here is an example of receiving lives:
at the end of this level you'll see how to answer friends requests:
Hey! Would you like to give us your opinion?