The most frequent use of according to is when reference is made to external evidence to support a statement or an opinion:
According to the safety experts, it was all right when they left it.
It’s the same in every block, according to Cliff, the caretaker.
This delay, according to Mr Mckay, probably violated federal law.
It’s going to be delayed, according to what Nick told us.
According to is frequently used to refer to statistics, official reports, surveys, opinion polls, studies, research, etc., especially in more formal contexts:
According to a recent report by the National Food Alliance, children are being saturated with advertisements for sugar-rich confectionery.
And regional government, according to a poll taken last month by Gallup, attracts the support of less than one in three of the public.
Note that according to refers to evidence from someone or somewhere else. As such, it usually has a third person referent. It cannot be used to refer to one’s own views or statements:
In my opinion all those sites should be made green-field sites.
(According to me/according to my opinion, all those sites should be …)