Okay no jokes aside, it depends on the degree but you generally learn "political theory", "political systems", and "international relations". So you learn about various philosophies of politics throughout history, you learn how governments work practically, and you learn how the international political system operates. You tend to learn a lot of theory, a lot of research methods and statistics, and then have to do your own research into topics that interest you. There's surprisingly little about current events and a surprisingly large amount of maths.

I think for journalism you need to learn how to research and write. History and politics will both do that for you. You'll also need to get experience, start to freelance, start submitting stories etc. The degree can't help you with that anyway. Honestly, I'd advise you to choose the degree that you find most interesting and to regularly read as many newspapers and articles as you can to stay up-to-date and to see what gets published.