To obtain your initial rating for each time control, you must play World Chess rated games with World Chess rated opponents. As soon as one of those games is a win or a draw, you must play 4 more FOA-rated games*.
*This means that the count down will only start after a game which is a win or a draw. Remember that those 5 games should be with a World Chess-rated opponent, so if, for example, two players with new status are paring, their game will not be counted.
When you sign up, your rating on World Chess will appear as "new". This shows to other players that you just joined, and it also indicates that you are still acquiring your rating.
It’s also very important to your opponents — when they play against you, their rating will not be dramatically impacted by a loss (or a win), but they will help you get a permanent status.