According to works as a preposition, a multi-word one built from a verb form plus to. Use it to name the source, basis, or authority behind a statement, like naming who a rumor came from.
The delay was terrible, according to the passengers. Here the passengers are the authority the claim comes from, not anyone the delay happened to.
The nearby trap: according to does not mean in agreement with. It names where information comes from or what a statement is based on, and it does not by itself convey approval or correctness. Saying According to the forecast, it will rain tells you the forecast is the source of the claim, not that the forecast is right.
The two uses split cleanly. According to can report a source, meaning where the information came from, as in According to the news, the bridge opens on Friday. It can also name a basis, meaning the standard something is judged or sorted by, as in The books are sorted according to size. The first sentence says who the claim came from; the second says what system the sorting followed. Once you can hear that difference, the two uses stop looking alike.
When according to reports a source, it tells you who the claim came from. Take According to the news, the bridge opens on Friday. Here the news itself is the source of the information, the authority the opening date is credited to, and the phrase works as one unit to attach that source to the statement.
wrong_result. The books are sorted according to size. This one names a basis, not a source, so it would fail if the hook asked you to spot a source. Try the other sentence instead, and the distinction will stick.
Two quick uses
According to the news, the bridge opens on Friday. The phrase points to the news as the source of the claim. If the opening slips, the reporter is not to blame; they were only passing it along.
The books are sorted according to size. Here it names the basis for a classification, not a speaker. Small shelf, large shelf, and the tallest ones at the end.
Not the same as in agreement with
According to does not mean in agreement with. Its core job is attribution: it names where a claim comes from, so according to John, the shop is closed only reports what John said. It never tells you whether anyone approves of the information.
One fixed expression blurs the line. Everything went according to plan means events matched the plan, a comparison sense locked into that phrase. In normal reporting use, though, according to the plan, we leave at noon simply states what the plan itself says.