QUOTE(jimlim007 @ Feb 9 2018, 01:41 PM)
btw, as i play ranger, should my helmet, suit, glove and boot must contain Armor or contain Evating? and i not able to asnwer your question about them gems, because i am still blur about gem in my item socket; many time i got corrupted gem or dark green gem, it did not stated for Bow, i really do not know whether those gem is suit for ranger or it actually for melee or spell hero.
Armor & Evasion debate is a long standing topic since the dawn of time; due to how the game designed in a weird way unlike others that are more straight forward.
Armor = percentage physical reduction. Evasion = percentage evade attacks & crit.
Both get diminish the higher level you get, which means harder and harder to maintain high percentage.
The usual debate is, armor is not good enough for big hit (eg: boss), and evasion is RNG - if it fails you're in trouble.
So, basically, we don't just use 1 layer of defense. Instead we have multiple, block, curse, immortal call, max elemental resistance, convert physical damage to elemental damage (which will need to go through your elemental resist, giving further reduction), or plain old manual evade...
Regardless, we always MAX out elemental resistance and as high HP (or energy shield for that type of character build) as possible to provide bigger buffer.But in a nut shell, we don't generally care much about armor/eva until later game.
What's more important are the mods they have, and socket links.Most corrupted gem are useless, but keep it for vendor recipe. 7 corrupt gem + 1 atziri map fragment = 1 Vaal Orb.
The way how you check if they are compatible with each other is simply by
checking the tags and the description obviously.
Most gems are compatible across many different setups, so you do have lots of option - it just a matter of min-maxing or which gives more dps than another.
Study the picture below (lots of typo...):
If it does support the skills, a little tag will appear on the hotbar icon as following example.
If nothing appear, means it is not supported.

Sure, the more support gems you link to a skill, the higher the mana cost will be to cast.
We get around this problem with several methods:
- low level, use Elreon's rings. They decrease mana cost by fixed value.
- suck it up and spam mana pot
- get mana leech on passive tree, we don't use "mana leech" or "reduced mana" support gems, they are complete waste of socket, better use your socket for more dps
- get around mana cost with certain interesting mechanic like "cast while channeling"
QUOTE
Just come across this game. Is it a good time to start? What are the best class for leveling/farming?
There is no such thing as best class
Because
failure or success of your character depends fully on YOU. There is no pre-defined skill trees like other games.
A skill looks boring by default doesn't mean it will be boring after you add some support gems or certain unique items, drastically altering the behavior of those skills.
Try many skills, pick one that you
feels good 
, find some build guide for reference and go from there.
Or go Youtube/Twitch and see people play, find something that you feels COOL and learn how to build that kind of character. If you don't see many people use a particular skill on one class, pretty much means that skill isn't very optimal for that class, but better optimized for other classes. Obviously not many going to play spellcaster on a Marauder, or a bow build on a Witch because of their starting position on the passive tree; but if you want to make it works, sure,
you absolutely CAN!This post has been edited by digitalifelesss: Feb 9 2018, 05:15 PM