The SPA represents the Portuguese authors of all literary and artistic disciplines. SPA authorizes the use of the works of the copyright holders it represents (domestic and foreign , whether authors, successors or assigns), sets the conditions for such use, charges the rights corresponding to such use, shall distribute the amounts collected, after deduction of commissions, by the holders of the respective rights and in addition, it performs social, cultural and mutualistic functions.
Music Publishing is the business of protecting and promoting song copyrights and collecting the royalties that these copyrights generate. Think of a song as intellectual property (it's an original piece of art!), and music publishing as the business that makes sure that songwriters get paid a fair compensation when their intellectual property is used by companies. Those companies could be record labels (mechanical royalties), radio stations, bars, and restaurants (performance royalties), or film studios and advertising agencies (sync license fees), and many more.