It was difficult to coordinate our steps-his halting,mine impatient 是一个分主句,
because of that,we didn't say much as we went along是第二个分主句,
and连接了这两个分主句使之成为一个句子
because of that是第二个主句中的原因状语从句
that指It was difficult to coordinate our steps-his halting,mine impatient
第一个破折号起解释说明的作用,指步伐难以一致的原因
第二个破折号起引出结果的作用,指因此我们在同行的路上并没有说很多话