Simple! First off, spawn into any world, even the tutorial world will do, cut down some logs and craft these into wood, make a crafting table and one stick, make sure you have 6 wooden planks left.
Go into the crafting table and craft a sign, it will be located in the decorations section. Once done, place it using
, it can be put on a wall or on the ground, achievement unlocked!
Go ahead and add a little message if you wish