At the beginning of your journey in Path of Exile, every character you create will have two basic resources – life and mana. These two are pretty straightforward – life represents how much damage you can take before you die and mana is used for casting spells and using auras.
You scale the amount of life on mana using items with such mods as (+ x to maximum life / +x to maximum mana or %increased maximum life/mana etc) and using passive skill tree mentioned earlier. There is another option – Energy shield.
Energy shield is like a barrier that absorbs damage before it gets to life – for example, if you had 1000 life and 2000 Energy shield, monsters would have to deal 2000 damage to you before they get to your life, so effectively you have 3000hp.
But there is one important thing you should be wary of when using Energy shield without some unique items or keystone – by default chaos damage can directly bypass it and attack your life while ignoring your Energy shield – that’s why most Energy Shield builds use Chaos Inoculation (widely known as CI) keystone that turns your build into purely Energy Shield character (The drawback of keystone is that you have maximum life of 1 but you are immune to chaos damage).
While talking about life, I will also give a little explanation about flasks in this game. There are two big categories of flasks – recovery flasks and utility flasks. The first ones provide you with the ability to regain health and mana (or both when using hybrid life+mana flask) and utility flasks give you various other buffs such as movement speed, resistances, damage, defense and so on.
When you are playing Energy shield builds, you have no option of using life flasks to quickly regain health as you do have when playing life builds. Like other items, there are unique versions of flasks, some are very strong and can boost power of your build by quite a bit. You can see a few flask examples in the image below, but you can always visit PoE Wiki and see the list of all flasks.
There’s a lot more players guide on https://www.u4gm.com/path-of-exile, so be sure to check out if you need some guides.