Why this matters for your research: Every news organization has a perspective, not necessarily an agenda, but a point of view shaped by ownership, audience, and editorial culture. That doesn't make them untrustworthy, but it does mean you should read across sources.
A useful habit: if you read a major story in one outlet, find it in one with a different political lean and compare how they frame it. What's emphasized? What's left out? That comparison tells you more than either story does alone.
The Ad Fontes Media Bias Chart maps hundreds of news outlets by both political bias (left to right) and reliability (original reporting vs. propaganda). It's a good starting tool, not a final answer, but a useful compass.