Path of Exile is a unique beast, it’s certainly something to satiate your pallet if you’ve been starving for a new ARPG to play, and something you’ll want to come back to if you ever stop playing.
Every few months there are new challenge leagues, which offer new content and gameplay elements exclusive to that challenge league. These are complete separate from the main game, you need to start from scratch when playing these leagues.
I strongly recommend Path of Exile to any ARPG fan out there, it’s like if Diablo 3 was a good game and didn’t cost any money to play.
Skills are obtained in the form of gems through vendors, as quest rewards, and drops. They can be put into sockets of a matching color(red, blue, green) if your character has the stat requirements, giving you usage of the skill. These skills cover everything, melee attacks, ranged magic, pets, and ect.
Instead of a skill tree, you have a passive tree, these passives can give you more str/int/dex, health and mana, damage, and other various special effects that can change how things work. For example Marauder is closest to the Blood Magic passive, which removes all mana, making skills spend and reserve health instead.
Any character can use any weapon and armor you want, they just need to meet the stat requirements.
Anyone who says that you either need a lot of health, burst damage, or anything else, is lying to you. You only need what the build you’re going for would require.
Character respecs are not easily avaliable, by about level 50 you should have gotten 12 respec points from story quests, beyond that you need to use an Orb of Regret to get more.