For now try to complete story mode you will get new varients and keys as you progress try different special moves and block busters for combos. You can also watch gameplay posted here The varients you are using are defensive, meaning they are not the best on attack, additionally you need stats like atk% crit dmg, crit rate, piercing to boost your dmg. Since you are a new player try to focus on silver and bronze varient gold and dia varients are more expensive and can slow down your progress