The way to the finish line is full of shortcuts and traps. You'll find Ladders, that will help you move faster, but also you'll run into Slides that will make you move back.
The first time you land in a square that has a Slide, you'll be able to avoid it by watching a promotional video or by paying with coins. Next time this happens, you'll be able to avoid the fall using coins, if you have any.
Remember you can also use the Shield Powerup, that will keep you from falling.
Cheer up! If you fall down a Slide, you won't lose your turn.