Here I am!
Summary
First off, Mabinogi does things rather different then a lot of MMOs. Chief among them, and indeed what most of the mechanics revolve around, is rebirthing. For your first 100 cumulative levels, you can do it once your character has aged more then a year. Week in real time.
After that it's more then three years I believe. Three weeks in real time. Age happens every sunday, so this isn't a solid thing, but it's close enough, you'll get the hang of it. Rebirthing returns you to level 1, and makes leveling easier. Levels get you AP, which you use for skills. AP and skill ranks are retained through rebirths. In your first rebirth you probably won't be able to solo ciar (easiest non tutorial dungeon) without issues, but you will slowly gain power.
But that's not all there is to it. You'll always be rather fragile, and combat revolves around avoiding damage rather then facetanking it. For instance, countering an attack results in no damage to you, defense (the skill) greatly lowers damage, etc. Generally if you're taking triple digit damage for more then a single hit, you're probably dead. Maybe less then that early on!
Combat as a result has a rather high personal skill entry point. You'll need to learn the ropes (the topic can help with that, as well as people in game), and get windmill (an offensive skill) to rank 9 asap. Windmill is important because it functions both as a powerful AoE attack, and a defensive skill, as it knocks back enemies. At any rate, onward to more technical aspects of combat.
First off. I highly reccomend taking melee combat skills on some level. If you want to be an archer or a mage, that's fine, but have a plan for when enemies manage to close in, because they will. These plans usually involve counter/windmill. Hence, ranking melee skills. Notably windmill, again. Melee is also the easiest to learn, which is a huge help. Feel free to branch out once you've got the ropes, again, although you'll be quite a bit more deadly if you focus on a specific skill until it's capped, then moving on to another, etc. On to practical combat explanations.
An example scenario: You're in a smallish room, two goblins. One of the goblins attacks, you counter, it's almost dead! You run in to finish it... And then get punked. Rule one: Never engage an enemy on it's own terms. You want to hit them after they've hit a defensive skill, or just flat out kill them via counterattacks. Killing them before they notice you is very good too. Leading me to part two...
Another: Same situation. You manage to outright kill the first goblin before it notices you. Hooray! The second goblin however, notices you, and you fail to realize the severity of the situation one way or another and again, get whomped. Rule two: Always assume the enemy will completely maul you if you get attacked. Have defense/counter/windmill or at the very least an escape plan when an enemy comes at you. This becomes less universally true as time goes on, but it's very very true early on, which is naturally when it matters most.
And finally: Same situation, but one goblin is an archer. The first goblin attacks you and then the second goblin also aggros onto you and starts aiming a shot. You're in trouble now! This is the situation that kills a lot of people after they've got the basics down. It's called multi aggro and there's no real easy answer for it, as it is a very VERY broad problem that can occur in any number of situations. You will need to learn how to handle it, one way or the other. In the case of archers (ranged enemies tend to multiaggro the most early on), nailing them with magic, or just flat out bumrushing them is the easiest way. Once all the archers are dead, you're back to basic combat and the situation is no longer dangerous. Having friends along has obvious benefits for it, but it's still possible for everything to suddenly go to hell, so it's important to learn how to deal with it in a solo situation. This is going to be your first combat wall, and as a result I'll leave it there. You've been warned! Don't lose heart just because it kills you, because it will.
A lot.
Crafting is rather basic. Simple put in objects, recieve crafts, BUT crafted items have various statistical bonuses that make them slightly more valuble then normal gear. Not typically worth a whole lot, but if you are of a crafting persuasion, the game just has a certain magic about it that makes crafting very satisfying. I can't fully explain it. You will have to kill stuff to get some crafting items. Take note. Leather is the most notable thing.