to set in place: to put or lay something, and by extension to appoint, name, or issue a command
At its root this Aramaic verb means simply to set or place something: to lay a beam in a wall, to roll a stone over the mouth of a pit. From that plain physical act the word stretches in several natural directions, the way English "set" or "put" can mean far more than moving an object.
Most of its uses in Ezra and Daniel are not physical at all. Its signature use is a fixed royal phrase, literally "to set an order," which means to issue a decree. Almost every time a king in these books commands something, this is the verb, so the word carries the weight of official, published authority. The same phrase turned toward a person means to pay heed or give regard to someone.
The verb reaches further still: to set a name on a person (to name or rename them), to set someone in an office (to appoint), to set the mind on a task (to give it one's full attention), and to set one thing as another (to make or turn it into that). All of these are the one act of setting, aimed at different targets, which is why a single small word does so much work in these two books.