I wouldn’t worry about prefixes too much, at GCSE you should find that
“-ide” is when an atom becomes an ion due to a loss or gain of electrons. Eg a chlorine atom, a chloride ion, oxygen atom, oxide ion. (negative ions / anions)
“-ate” denotes a polyatomic ion containing oxygen. The amount of oxygens depends on the oxidation state of the central element or its coordination number, but that can change. You can have chlorate (I) ClO-, where chlorine has an oxidation state of +1, and chlorate (V), ClO3- where chlorine has an oxidation state of +5.
Sulphate (VI) is SO4 2-, and Sulphate (IV) or Sulphite, is SO3 2-.
GCSE revision guides aren’t very contextual, and simplify things too much. At this level, -ide is for just a negative ion from an atom like bromine to bromide, carbon to carbide, nitrogen to nitride etc, and -ate refers to a polyatomic ion with oxygen. Eg Nitride ion is N3-, and Nitrate (V) ion is NO3-, or carbide to carbonate etc.