SDD Team concept, discussion, and explanations
The current most used SDD team consist of Dragoon Drake (equipped with lifesteal skill rune), Witch Doctor Matilda, 1 Hero with lifesteal aura (Blood Knight Leon & Darrion, Gladiator Drake, Samurai Miu, Dragoon Eliza), and Spirit Walker Kahuna.
The variant consist of Dragoon Drake (equipped with double strike rune), 2 Heroes with lifesteal aura, and Spirit Walker Kahuna. This one is less reliable than the first variant though.
The composition is used mainly because it can reliably trigger from the start of the battle till time out. And you can just focus your best equipment on Drake as the other party member only needs to survive if Drake or Kahuna stopped triggering.
The downside of this team is that it is only useful on certain occasions. You can't use it for arena, you can't use it for daily event, and it's performance is quite poor on stages where your enemies are far away from your starting point.
The other composition is Archers team. It's harder to build, require more resources and time, but can be really reliable and usable outside raid too.
But as new player, you shouldn't rush things out and build your team at your own pace.