From the Super Mario Wiki
Alpine Skiing is an event in the DS and Wii version of Mario & Sonic at the Olympic Winter Games. In this event the player must ski down to the bottom of the mountain going through a number of flag gates. If the player misses a gate, two seconds are added to the run in the Wii version, and 3 seconds are added in the DS version. The player that gets to the bottom in the least amount of time wins.
In this event the player has to ski down though total of 36 gates. This only appears in the Wii version.
This event is similar to Downhill except there a total of 28 gates (24 in DS) and the course is shorter.
Start – Flick the and down.
Turn – Tilt the and left or right.
Slow Down – Tilt the and up to brake.
Start – Touch and hold the on the Touch Screen on and flick down to accelerate.
Turn – Touch to change directions.
Crouch – Slide down on the touch screen.