Who in the organization signs players in Major League Baseball?

In MLB, how exactly does a team go about signing a player? I understand that the people and/or process involved is unique to MLB. I know a scout does the searching for "draftees" for which whom is eligible based on a criteria, but as far as the actual decision to sign a player goes, how does a team go about making that selection? Are there many people involved? Is it a different process involving different people in signing the player if the player is a rookie, a free agent, or to be acquired via trade? Is there one person whom has more influence and/or actual weight in making the decision? (etc, etc.) *I am particularly interested in the person(s) described above in the New York Yankees organization (especially since I am unsure if the individual[s] vary from team to team in MLB). Would greatly appreciate the help, thanks a lot!