The company's career page was flooded with applications after the new position was posted.

was 是 be 动词的过去式，表示被动语态。 flooded 是动词 flood 的过去分词，原意是"淹没、泛滥"，这里用作比喻表示"大量涌入"。 with 是介词，表示"伴随、带有"。 was flooded with 这个被动结构表示"被...淹没/充斥"，在这里形象地描述求职申请数量之多。