This is the response I gave to a similar question a few months ago:
International Relations is the academic study of international relations (what goes on in the world) - this can be relations between states, between states and non-state actors, between religions; the study of international trade and its impacts on domestic and international life; the study of the role of international law; the causes of war; terrorism; 'normative' issues like human rights; international development, forced migration etc..
There are only a handful of universities in the UK (including the one I study at) that offer a single honours degree in International Relations. Most universities offer degrees in Politics and International Relations. In these degrees you'll study modules in IR and in Politics. Politics classes tend to be concerned with democratic theory, comparative political systems, electoral processes, the role of the media and the like. While IR is by nature international in focus (though it doesn't take long to realise that the distinction isn't quite as clear as all that).
What differentiates IR from human geography, history, economics, etc., or a degree in reading the newspaper, is its basis in theory. This is not to say that economics is not based in theory, it is. Just that theories of International Relations are different from theories of economics, or from historiography. Theories of IR aim to equip you with tools to answer questions of how we should understand the world and how we should act in it.
There are many different theories from Realism and Liberalism to Constructivism, Marxism, Feminism, post-colonialism, to name a few. Any IR degree that calls itself an IR degree will have classes on IR theory, as it forms the academic basis of the subject. However, you don't just study IR theory.
You study issues in international politics (including those listed above). The actual issues you get to study will depend on which university you go to as it will depend on the research interests of the faculty. If the faculty has a number of regional specialists then there will be courses on the Middle East, Africa, Latin America and Asia; practically every department offers courses on terrorism and security, international political economy, and conflict resolution. If the department has a strength in political philosophy then there will be more broadly conceptual classes on the history of political thought.
I hope some of this info helps. IR is a broad subject, with its own theoretical base. This can be confusing/daunting when you are trying to figure out exactly what it is as a subject, but also great because it gives you the opportunity to explore those international issues that are of most interest to you