有关推荐信的问题

刚刚登陆了tud的官网，上面说需要两封推荐信，一封from an official of the faculty from which you obtained your degree，一封 from your employer or another person in authority, e.g. your Bachelor’s thesis supervisor.我想请教一下这两封信有哪些不同要求，要怎么准备？

一个找学校开，一个找你组里的老头子开呗