Hi,
An element’s atomic number tells how many protons an atom of this element has. Protons have a positive electric charge, while electrons have a negative one. If an atom is electrically neutral (as in this case, otherwise it should have been specified) the number of protons and electrons are equal. So, an atom of the element would have 59 electrons.
Hope this helps! If my answer was not clear enough or you’d like further explanation please let me know. Also, English is not my first language, so I’m sorry for any mistake.