Where are sedimentary rocks found?
Clastic or carbonate sediments usually accumulate in low areas next to continental land masses and over time become turn to rock (called lithification) in sedimentary basins. Basins can be found on continents or next to continents in the oceans. See pic of sedimentary basins in Australia. They can be of just about any geological age too. Geologists usually explore for oil and gas in sedimentary basins.
Technically, the term "formation" in geology is a sequence of sedimentary rocks that have similar characteristics, some times color, and can be easily mapped in the field.
As some people might think, a "formation" is not any unusual erosional feature in a series of rocks. See 2nd pic. The yellowish rocks look quite different from the underlying reddish rocks and so each would probably be defined as different "geological formations" regardless of how they looked!