Beginner Tips: Parties
For a beginner, it's recommended to have AT LEAST ONE HERO FROM EACH ROW (Melee, Magic, Ranged) in your main party.
You will usually want one tank at the front of the party to absorb damage. This can be a hero dedicated to tanking, or any Melee hero equipped with defensive gear.
A beginning player will only need ONE PARTY OF FIVE HEROES. Most players recommend focusing on a balanced party to begin with.
You should focus on raising the heroes you use to purple frame with Orbs to begin with. Once you're satisfied with your team or want to try to use new heroes, you can branch out at any time.