其实差遣现在已经不怎么用了， 差遣主要是指以前皇帝或高级官员委派低级官员去做事

就是差使某人到某处做某事。

甲任由乙差遣。意思就是 甲由某个人（指甲的上级领导）委派给乙，任由乙调用。

在生活中一般不会用，因为往往被差遣的那人地位/职位比较低，不太礼貌。

It means someone is arranged/ordered to do something by the leader or boss, or someone arrange/order the others to do something, usually appeared in written language.