Yes, just like that. Masteries are for Equip stuffs but you can only equip one of it. Also when you hit level 30 in any class it'll unlock their specific Skill Mastery ^.^
You get Job Change menu by start, mostly new Jobs will be automatically unlock when you hit level 20. Every 10 level you gain a Mastery Passive and all Characters now have 3 or 4 unique classes, pretty unique skills, you can even convert your HP to TP, TP to MP, MP to HP :D