When you start playing Undead World: Hero Survival, you will use the default formation. As you level up and unlock more features, you will gain access to the Formations tab where you can view more options. Continue playing, levelling up, and collecting resources, and you will level up your Formations options to unlock more and more ways to organize your team for enhanced battle strategies.
Generally, it is best to place Range heroes on the back line, as their skills allow them to hit targets from farther away. Tank heroes are a great choice for the front line, as they can take more damage. Learn about hero types in Undead World: Hero Survival.
Sometimes, you will encounter a game effect that refers to "the hero at 1st position" (or 2nd, 3rd, etc.). Tap Formations to access the formation diagram so you can tell which position is affected. This will help you to strategize by placing the correct hero in an affected position.