What does it mean to recruit personnel agents in universities?

Some are recruited to work as university counselors or other administrative offices. How can the personnel agency be formally established? The so-called personnel agency means, for example, that unit A wants to recruit people, and unit A goes to unit B that is qualified to engage in personnel agency, and after recruiting in the name of unit B, it is sent to unit A for work. After signing a labor contract with unit B, the personnel engaged in this work will be sent to work in unit A.. And managed by unit A, with the nature of labor dispatch. It can be said that it is not the official establishment of unit A! for reference only