How do I play a card if it has two colors within the one mana symbol in its cost?
Mana symbols such as  are called a hybrid mana cost. You can pay that cost with either of the 2 colors shown. Here is a brief summary of hybrid mana rules:


  Hybrid mana symbols represent a cost that can be paid with either of two colors. For example, a cost represented by the  symbol can be paid with one white mana or one blue mana. It’s both a white and a blue mana symbol, and a card with  in its mana cost is both white and blue.