politics and policy

Politics (usually singular but always with -s, (see here) is used to talk about government and related ideas.

• I don’t know much about politics, but I don’t think this is a democracy.
• You talk beautifully – you should be in politics.

Policy is used for people’s rules of behaviour (not necessarily connected with politics).

• After the war, British foreign policy was rather confused. (not … British foreign politics …)
• It’s not my policy to believe everything I hear.
• It’s the company’s policy to employ a certain number of disabled people.