The first thing you will have to do is unlock the Phoenix 250cc bike. To do this you must pass the A license test, unlocked at 75 total medals.
View "Schools Out" guide for additional details on completing the license test.
Now, just go to "Walk in the Park" and complete all 5 beginner tracks using the Phoenix 250cc, and the achievement is yours.
Faults are allowed, and gold medals are not necessary.