It's a sandbox game, probably best compared with The Sims series.
There's a building side to things. There's gameplay loops you go through to earn the things needed to build, and as you play more, there's more options to do it more efficiently, and more you can accomplish as a result.
There's a creative/build mode and a survival/live mode where the former removes the cost of obtaining the resource. You just built and create.
There is no ultimate end goal in either game, though the above ender dragon and subsequent poem in this game can sort of be seen as one. But the game is still very much a sandbox. And when it comes to games like this, if you have to ask what the purpose is, it's probably because you aren't coming up with one yourself and therefore it's probably not a game for you.
bruh just slap the sword at fire monster and purple teleporter craft some nice lookin shiny eyes of edneer reight cllick the skiy and run for miles to reach undergrond masze and find portal jump in and kill big black ezz to kill ender suss
Too beat the game you have to kill the Ender Dragon and go through the exit portal.
Prior to Release 1.0 some players would consider getting a full set of diamond armour beating the game. some people would consider getting to the farlands beating the game but most people never could or would even try!