Basically all a Senate hearing is is the normal process by which the body of the United States Senate functions and exactly what they do to carry out their duties in a legislative body.
Most people would not think that there are four different types of hearings and would only think that they all fall under one type of hearing, but this is not the case as the Senate has different rules and procedures to follow each and every type of hearing that they have.
For example, all that Senate confirmation hearings are are simply reviews similar to job interviews in which the Senate votes on whether or not someone, who has been appointed, is qualified to hold the post that the President has appointed them to.
In this instance all they simply do is ask questions for however long they feel, and eventually have a vote to decide whether or not the person should hold the position.
Unlike the Legislative Hearing, they do not have their decision go through review of the President or the House, as they are the ones that ultimately decide whether an appointed person is fit to hold office.