After completing the first duel of the 5D's campaign, which teaches you how to Synchro Summon, play the second duel with the story deck and you're very likely to unlock this achievement naturally. The easiest one to do is Junk Warrior, as Junk Synchron lets you special summon a level 2 monster from your GY when it's summoned which will instantly fulfill the requirements to Synchro Summon Junk Warrior. You don't have to win the duel, the achievement will unlock immediately upon performing the Synchro Summon.