Lives are used to play levels. 

"Full" means 5 lives.

Gems are earned playing levels. You'll get more gems for having moves left over! 

You can spend gems on extra moves, to fill up your lives when you're out, or to speed up things in The Business.

Coins are earned by winning levels.

You'll need them to complete tasks for each vehicle.

Cash is earned by flipping cars and completing tasks in The Business.

Use it to buy and upgrade buildings, and expand your land.

XP is earned by completing tasks in The Business.

Needed to level up and unlock new buildings, decorations, and features.