One of the easiest ways might be to have him take a look at an app like GroundNews, which displays biases of publications and shows blindspots in the media according to political lean. The biases and differences in headlines, presentation, language used, and what stories get reported at all by any given publication become very apparent.
Words to watch out for are things like "attacked", "bashed" or "slammed" instead of "criticised"; "forced" instead of "chose", eg "company forced to cut jobs"; "muzzled" or "gagged" instead of perhaps "censored". The implied violence charges the story emotionally, it's the most common form of news manipulation. They're trying to make you feel - usually fear or anger - rather than think.
My only complaint about Ground News (and most media bias meters in general) is that factual papers will almost always be listed as left-leaning. Because the Overton window has shifted so far to the right that cold hard facts presented exactly as they happened with zero spin now has a left-wing bias.