Path of Exile is something that most people can't learn entirely at once, even for the most Hardcore of players. But for those who are either just starting out or have been playing for one week or two, the game seems very horrible and inaccessible from Path of Exile Items to character builds. The ability to choose which league you play in is one of the things that make Path of Exile fun. These leagues give the game more variety and challenge in making players choose who they want to play the game, whether they can do at a leisurely capacity.
Firstly, you encounter options for which Gateway you want to play in when you log into the game before you get to choose which league you play in. Generally, you should pick the closest one to you, but you should consider the ping numbers to get the best one. By the way, you can pick up every PoE Currency you meet, maybe some currencies are useful for you.
They don't express separate servers like other MMO games as you can communicate and play with other players from all over the world in whatever gateway you're in, but your choice affects your latency.
Standard and Hardcore
In the character selection screen you choose your league then, with two major options to choose from. Standard, or colloquially known as softcore, is the baseline wherein you can play to your heart's content, without risk when your character dies. This is not so in Hardcore leagues as you have to do everything under your own power to survive while getting stronger.
In Hardcore, the difference is that if you die, the character and poe items in your stash will be transferred to the Standard league, which is like being booted out as eternal punishment. If you wish to be a better player in this game, then you should work into the Hardcore league. The poe exalted orb is the shortcut to help you back to the Hardcore league.
Also there are time-limited leagues where you try to become as strong as possibly and compete against other players to see how good your game knowledge and skill are. Usually these challenge leagues last for a long time, after which new challenge leagues are established and the cycle repeats.
In the other leagues, since it's all about who farms and grinds the hardest, things tend to stagnate after a while. It's a great idea that has proven to be good in practice. If you just start out, you can't get ahead and become the best in the league unless you grind 24 hours every day and abandon other things, and maybe it still won't be enough.
You all start off from absolute zero and play as optimally as possible in challenge leagues. Players who usually play in challenge leagues are those who have played standard and hardcore for a considerable of time, so they know quite a bit about the game. They know what to do and where to grind, as well as which character build works best for their intended goals.