In Path of Exile, there are some players that coming back after about a few years. A few years is enough to change many aspects of a game, so, for them, PoE may unfamiliar. I Hope the following guide will help these players.
Gearing and leveling has changed massively. The Forsaken Masters will allow you to add needed affixes on rare gear, for example if you find boots with move speed and tri resistance you can use the masters crafting benches to add life to the boots. On top of that there is poe.trade where you can buy items from players very easily.
Using poe.trade you can fully gear a character that will steamroll most of the content in the game for sometimes 1 chaos per item. Finding and amending items, especially for leveling and entry level mapping has been trivialized.
You can sell a full set of identified or unidentified rare items to the vendor for 1 or 2 chaos, if the items are from a level 60-74 zone. You can use the chaos recipe to easily gear up at any time.
If you're going to try to use old characters in standard make sure you type /passives . The quests and free passive points have changed so you might have to go back and redo the entire story line, or get somebody to give you a portal in order to get all the available points.
You will also need to complete lab trials scattered through the acts in order to ascend. It might be more annoying to update old chars in standard then to level a fresh one in the league. If you ask for help though you can probably find somebody that will provide you with portals easily enough.
If you're going to use one of your 3 characters, I would use one of the duelists to make a generic slayer/sunder build. This will leave you with another duelist to do attack stuff and the templar for other builds. Slayer sunder is solid and cheap and you should have no trouble doing uber lab and crush most maps.
Download pathofbuilding, it's a third party program that allows you to create and import builds. Path of building gives you better DPS and other stats then the in game tooltip and its widely used for good reason.
Watch youtube videos, streams, check the wiki for the info on leagues you missed. There is an atlas for maps, which you can potentially screw up just like the passive tree. It helps to have a plan going in since mapping is more specialized. Or you can visit https://www.u4gm.com/path-of-exile
, here are some guides and news related to the Path of Exile for most players.
You're always encouraged to play in temporary challenge leagues, so look into the rewards, etc and see if its worth it for you to create a new char now in Beastiary, May 4th for the flashback event, or even June 4th? for the next 3 month league.