English (Source)
Your Commander has already access to several towers. The first two are unique to your Commander and define their playstyle, many times being purely supportive. Build a few towers within range of the building, and make sure to build one which can actually attack.
Chinese Translation
你的指挥官已可使用数座防御塔。前两座为指挥官专属并定义其玩法风格，很多时候仅提供支援。在该建筑的范围内建造几座防御塔，并确保至少建造一座能够进行攻击的防御塔。