Mauro, Start and begin can be synonyms. The race starts. The race begins. In both of the above sentences the activity of the race has just begun. This would generally be when the runners begin to move after the starter pistol has been fired. The race is getting started. In this sentence "started" is an adjective. The race is is the process of reaching the condition of being "started". The runners may be fidgeting in the starting blocks or the runners might have just made their first steps after the pistol was fired. In any case "to get started" refers to the process of starting and not just to the moment when the pistol is fired at the beginning of the race.