You'll need a total of 75 medals to take part in the A License Test.
To obtain a new drivers license you'll need to play through the tracks, skill games and tournaments to earn medals. Each medal you earn counts towards the progression bar and your new license. Once you've acquired the right amount of medals the new license test will become available.
The best and fastest way to obtain 75 medals is to get gold on all the beginner and easy tracks and then silver on the medium ones. Doing this will net your around 80+ medals give or take, so there's plenty of room for error. Once you've obtained enough medals, you can take part in the A License Tutorial track which will introduce you to some of the advance moves of the game