Lives in Candy Crush Friends Saga work a bit differently to lives in other Candy games.
You still have five lives, but when you run out you can only receive help from your friends when you have fewer than 5 lives already. To access those lives, just tap the heart icon in the top corner.
Please bear in mind that you can’t choose to accept just one life and store the rest. This means that if you have 0 lives, you'll only be able to accept five (if five friends have sent help to you). After receiving a life, you will also have the option to send lives to other friends!
If your friend sends you multiple sets of lives, you will only see one set in the queue. Once those have been accepted, you will be able to receive requests which are then re-sent.
If you have fewer than five lives, you will have the chance to ask your friends to help you. Alternatively, you could use the lives that you've already received.
Whenever your friends make a request to you for help, you'll see a little envelope icon on the heart icon on the top corner. Tap the heart icon to see the requests and give your friends the lifeline they need!