Your employer can't just pay you any salary they want. That's why there's such a thing as scales. These are fixed wage scales in which the minimum wage per sector is stated. In those scales you can also see how your salary can evolve. In some scales the salary evolves with your experience, so you'll earn a bit more with every year you work. In other scales the salary is based on your job title and the tasks you perform.
You can check which sector uses which scale on www.minimumloon.be. Good to know: this contains the -you guessed it- minimum wages. An employer can therefore also choose to give you a higher wage than what is stated in the scale of the sector.