• Don't stand in the red circles.
• If scary stuff is happening, hold block. Even without a shield, it greatly reduces incoming damage.
• You can join up to 5 guilds at once. In Game Setting > Social > you can also change chat colours for each individual guild.
• Trade Guilds help eachother buy/sell items through Guild Stores. They can also hire a Guild Trader, which is an NPC that gives access to Guild's store for anyone visiting. But you don't need the Guild Trader to trade internally! Go to any banker in a major city and select "Guild Store" - here you can trade with your guildmembers, regardless of whether the Guild has hired a Trader.
• Gear scales until you reach level 50 + 160 Champion Points ("CP160"). It's best not worry about farming or buying gear until that point, as you will soon replace it any way.
• Due to the existence of "Daily Random Dungeons" and their rewards, a lot of people you match with for randoms will be in a hurry. This can be very distressing, if you're the type of person who likes to take their time to explore and talk to NPCs. Consider gathering your own group of friends/Guild Mates so everyone is on the same page, at least the first time you go through a dungeon.
• There's no limit to how many crafting skills one character can have.
• Skill points, used to unlock everything from ultimate abilities to crafting help, are available through a lot of sources. Leveling up, ranking up in PVP, finding Skyshards, completing dungeons (first time quest), completing the Main Quest, etc.

Can X class play Y role? Can I use Z race for this class?
Short answer; yes. Long answer; yes, but not necessarily at the absolute best.

Any of the six classes (4 basic, 2 from DLC) in ESO can play any of the three roles; Damage Dealer (DD), tank, or healer. Healing used to be pretty one sided, admittedly, but ZOS has done a lot to alleviate this over the years, to the point where most classes have several skill morphs dedicated towards healing (where previously they were just different flavours of damage dealing).

With all this being said there are always higher and lower performances, but for the most part these only become relevant in high level gameplay. E.g. the world's best Stamina-Sorcerer-Damage Dealer will typically outperform the world's best Stamina-Dragonknight-Damage Dealer. The Class is simply (currently) stronger for DPS. These things fluctuate however, given new set releases and ability/race buffs and nerfs.
Furthermore, an Altmer (High Elf) Magicka Sorcerer will tend to outperform an Orc Magicka Sorcerer, because High Elves have racial passives that benefit magical attacks, whereas orcs are geared towards physical damage. See a full list of racial passives here.
Of course, these differences mostly matter in high-end gameplay. If you're not to worried about that, by all means play an Argonian, stamina necromancer, or whatever. You just have to live with the fact that you'll never quite be top tier in that role.

If you really want to min/max...

Damage dealing in ESO is usually a matter of keeping up Damage of Time effects (DoTs) and filling the room between refreshing these with a "spamable" - any direct, instant damage ability.
I won't go into a long list of which DoTs and spamables are best, but here's some generic advice for being a Damage Dealer.

• Hybrid builds are simply not viable currently. Throw all your attribute points into either stamina or magicka. (You can always "respec" to try out what suits you best).
• Remember that you have two weapon bars; you may use the same weapon type on both, or a combination of different ones.
• Use a food buff! Sustain (having magicka/stamina to consistently use abilities) can be tough. Get some food with magicka or stamina recovery, and keep that buff up!
• Use potions! In previous Elder Scrolls titles potions were typically an "ow ***!" button, not so much in ESO. As a Damage dealer, you pretty much want to use them on cooldown, to keep with sustain.
• The healer will heal you, the tank will keep the baddies away! Don't slot overmuch defensive gear or skills unless you have to. It's your job to make things dead!
• Pick the right Mundus Stone! This will typically be The Thief (increased crit chance) but sometimes an argument can be made for The Shadow (increased critical damage)
• As a rule of thumb, the best stats for damage are (in order): Critical chance, weapon/spell damage, max stamina/magicka.
• Try to achieve the two buffs; Major Brutality/Sorcery (+20% Weapon/spell damage) and Major Savagery/Prophecy (Physical/Magical Critical chance) at all times. In late game this is done with potions, but until then there are many sources.
• I made a list of relatively easy-to-get damage sets here. Don't worry about them until you're CP160 though!

Specifically Stamina DDs
Use Dual-wield (preferably 2xDaggers), twohanded (preferably Axe or Sword), and Bow. Multiple combinations work here, depending on gear. 2H/DW, 2H/bow, DW/DW, etc. Although bow/bow is typically hard to justify, and requires very specific gear.

Specifically Magicka DDs
Use Destruction Staves, preferably Inferno, x2. For Nightblades and Dragonknights an argument can be made for 2xDaggers on one bar, as these classes have skills that incentivize being in melee range any way.

Sources of Major Buffs

• Taunt the boss and stand still. Sorry, but too many tanks feel the need to run around all the time. A great many abilities in this game (both healing and damage) are ground-targeted, meaning they leave an effect on the ground in a specific area. If you move the boss, the healers/damage dealers constantly have to refresh these abilities, lowering group performance.
• This game has no "aggro" system. You use the two taunt abilities (Puncture from one hand/shield) or Inner Rage (Undaunted skill line) to taunt enemies. In big AoE fights, usually try to control enemies with stuns/roots rather than getting taunts up on everyone.
• Face the boss away from the group, if possible. Many enemies have "cleave attacks" that strike everyone in front of them, try to make sure that only hits you.
• You don't have to block ALL the time, sometimes it's enough to just block the heaviest attacks (the ones where the boss does a wind-up or channeled animation).
• Make sure to bring some abilities that help with sustain. You need to restore stamina for blocking somehow!
• You don't have to be a max health, super tanky monster to survive Normal Dungeons! Get heavy armor, a onehanded+shield and just taunt the boss! Enjoy short queue times for random dungeons!

• Use a restoration staff! Most classes have abilities/morphs that are appropiate for healing, but these typically won't be enough! You want skills from the Restoration staff skilline.
• Healer is a magicka job. Sorry, not much variation here - there simply aren't enough stamina-based group heals.
• Contrary to other games, it's not just about keeping your party alive. You're also expected to help keep people's resources up! For Templars this could be Blessed Shards ability, but otherwise you want to use the Undaunted skill Healing Orb, which can be activated by allies to return a lot of resources (stamina or magicka). You're also expected to help supply several buffs to help deal damage, such as Minor Berserk from the Combat Prayer ability.
• Enjoy short queue times for random dungeons!