There are three different Hero roles:

Attacker: Your attackers are your best fighters. They're the ones that are going to deal the most damage, so smart players will put their melee Heroes on the frontline, giving them the best chance of landing a powerful blow on the enemies. For long range attackers, it's usually best to leave some distance between them and the enemy.

Defender: They say the best offense is a good defense, and we tend to agree. Defenders do just that - they defend. They can take a beating so the other heroes on your team don't have to. Place them up on the frontline and let them do what they do best.

Support: Support heroes are all about the team. They might not be as flashy as the attackers, but that doesn't mean they're not important. They're there to make everyone on the team better. Put them in your backline so they can give your team the advantage you need to win.