The gameplay in Terraria ranges from creating massive builds to defeating eldritch gods. Everything that happens in between is meant to make things easier for you to accomplish your goals. It can be easiest to digest what Terraria has to offer after understanding what the general objective is.
Every player will begin their world in pre-hard mode and work their way up to defeating the Wall of Flesh boss. This unleashes hard mode onto their world and an entirely new section of the game opens up. While fighting waves of enemies or fearsome bosses can be intimidating, every challenge in Terraria can be conquered with enough preparation.