Bestselling writer, Louise L Hay has a good explanation for this. Firstly we must love ourselves, and love ourselves unconditionally. We can only give away what we've got and if we've got love for ourselves then we can give love to others.
Louise says, "Look yourself directly in the eyes in a mirror and say, 'I love you - I really love you." Many can't do this - at first. But with practice the subconscious is programmed and you do learn to love yourself. You become loving, and your begin to act lovingly.
Loving acts creates happiness automatically. (No, I'm talking about sex here, though it isn't excluded) When we do something for someone else, without expecting anything in return, we are immediately rewarded by a feeling. Yes, a feeling. If, for example, it is an act of generosity that arises spontaneously, the reward is often greater for us than it is for the recipient of our kindness. Loving acts of this nature create immediate happiness.
You see, we identify with our thoughts. These thoughts often determine our acts. So if we come from love we create happiness, not only for ourselves but for those around us. That is the connection.