The correct answer to this open question is the following.
Your question is incomplete. You did not mention the US state you are referring to. We assume that you are talking about the Florida peninsula. If that is the case, then, the correct answer is the following.
The Northwestern highlands is considered to be the region of the border with the state of Alabama and Georgia to the North. To the south is the Gulf of México. This region includes two large cities: Pensacola and Tallahassee, the state capital. The largest river in this area is the Apalachicola River.
The coastal lowlands are the region of Florida also known as the coastal prairie, an area that is constantly affected by heavy rain and hurricanes. So there are flooding areas and mangroves. We are talking about the Florida Keys and the coastal areas of the peninsula, to the Atlantic Ocean and the Gulf of México.