If someone says, "according to the weather man, it's going to rain," that means that the weather man is the source of the information.
Like the word accord, according comes from the Old French acorder meaning "reconcile, agree, be in harmony." According and the word to seem to be in harmony, the one always followed by the other. The term according to can be used to attribute something reported — according to the news, the airports are closed (even though according to your friend, they're still open). It also refers to agreement with a plan. If you study according to your advisor's suggestions, you'll do well.