While fake news refers to fabricated journalism for a variety of purposes, media bias usually refers to what stories are covered, which sources are used, and the implications of how a given story is presented. Put simply, when people talk about bias in the news, they are usually talking about how liberal or conservative a news outlet is perceived to be.
These are some sources that can help with determining political slant:
This news site provides stories from multiple sources side by side in order to compare scope and nature of reporting depending on political leaning (left, right, or center). It also features the AllSides Ratings page that allows users to filter news sources by bias.
Pew Research Center -- Political Polarization
Survey data from this "nonpartisan fact tank" reveals which news sources are favored by people depending on political belief.