Politics (usually singular but always with –s) is used to talk about the theory and practice of government, the profession of government, conflicts between governing groups, and related ideas.
  • I don’t know much about politics, but I always support the [whatever] Party.
  • You talk beautifully – you should be in politics.
Policy means a “political line” or a rule of behavior (not necessarily connected with politics).
  • After the war, our foreign policy was rather confused. (NOT …foreign politics…)
  • It’s not my policy to believe everything I hear.
  • It’s the firm’s policy to employ a certain number of people with disabilities