In most 'normal' ionic compounds (ie compounds you're likely to come across at GCSE or A-level) the metal will be the cation and the non metal the anion.
You can get metallic anions (eg alkalides) and non metallic cations (eg protons- which you should know about), but in ionic compounds you can go with metal=positive and non metal=negative in general
So, please note:
metal atoms -> donate electrons -> positive charge (cation)
non-metal atoms -> accept electrons -> negative charge (anion)