How do editors "find out about" pressing stories or know what stories to run?
Finding out about stories often comes from just keeping track of people who are likely to make news; either media pursues the events, or the events come to the media. Political controversies tend to occur at political meetings, court cases, and so forth, the schedules of which are generally public, and someone will be sent to attend and take notes. A lot of news - cultural and sporting events, financial upheavals, et cetera - is often something that some party or another wants or is required to make public. Everything else gets covered by curious reporters following a personal interest.
Which stories make it through composition to print is - I think
- each editor's personal decision, using the criterion of how much they think a story is likely to capture the public's interest, and, therefore, how many people are likely to buy their newspaper to find out about it.