Details: At the main title screen scroll down and pick the Create Your Own Track option. From there pick your area this will give you some more options to scroll through at the bottom option is Random Generator! Now if you want something down and dirty quick for the achievement you can modify your options even further by choosing a "Mini" track length that should only be about a 10 second track. After it loads it will build and you will simply press the A button to validate/test drive your track. At the finish line you press the Y button to save the track, shortly after it is saved you will unlock your achievement.
Quick breakdown:
Title screen
Create Your Own Track
Choose area
Random Generator
Choose length
Press A
Test drive
Finish
Press Y
Save
(Achievement)