Happiness can be obtained by clearing Rubble and building more Decorations on your Farm. You can unlock different Happiness Milestone Rewards with the Happiness Points that you have collected.
Tap on the Daisy icon in the upper left corner to view the Happiness meter and the Happiness Milestones.
Related posts:
FarmVille 3: How does the Water Well work?
FarmVille 3: What is the Sky Race?
FarmVille 3: How do I edit Buildings and Objects?
FarmVille 3: What are Pets?
FarmVille 3: How do I unlock or upgrade Farmhands?
FarmVille 3: How do I use the Barn Storage?
FarmVille 3: How do I breed animals?
FarmVille 3: How do I use the Building and Decor Shops?
FarmVille 3: How do I plant and harvest crops?
FarmVille 3: How do I add neighbors?