Mining is the collection skill that matches up with both Engineering and Blacksmithing. Before you can mine, youll have to have a Mining Pick (which you can buy at any trade skill merchant), and will obviously need to train your mining skill up to at least level one. Then you can head out into the world and start looking for mining veins, which will let you unearth valuable metals.
Metal is usually going to be found in veins near mountains and hills - itll rarely be found out in the open areas of a zone. This means that metal collection will usually require a bit more dedication than either herbalism or skinning. You wont be able to create your own resources just by killing beasts, as you will in skinning, and you wont be running across your resources as you run around the bulk of a zone; youll probably have to dedicate portions of your time to "mining runs," as theyre called, and run around in zones where lots of metal veins are known to be located. A good example of this is the range of mountains stretching from just above Crystal Lake in Elwynn Forest all the way around to the Eastvale Logging Camp; if you run from one end of those mountains to the other, youll usually find a number of copper veins. Unfortunately, after a player gets three or four pieces of ore from a vein, itll disappear, and wont respawn for a few minutes. Thus, if you have the misfortune of starting a run a minute or two after another player, youre unlikely to find much of anything to mine. This can make mining something of a random pastime. Well see how Blizzard deals with the increased server population in retail; if enough people have a hard time finding mining veins, its reasonable to assume theyll either increase the number of them or decrease their respawning time.
Anyway, when you whack at a vein with your mining pick (if you have one in your inventory, all you need to do is right-click on the vein while youre standing next to it to do so), youll get a window showing you what youve mined. This will always include at least one piece of ore, but may also include various other items like pieces of rock or valuable gems, many of which will also be usable in your crafting profession, or, if not, then can be sold for good chunks of change.
Its the ore that you really want, though. Before you can use it, youll need to convert your metal ore into metal bars; this can only be done at a forge, which can usually only be found in towns with enough of a population to support an NPC blacksmith. (I.e. the smaller a town, the less likely it is to contain a forge.) When youre standing close to a forge, you can use your smelting ability to smelt the ore into bars, which are what youll need before you can start smithing items.
Now, when you have bars of metal, you can feel free to start making engineering items, if you have the other required ingrediants. To blacksmith, though, youll need an anvil; check the blacksmithing section for more details on that.
Skinning is the collection aspect of leatherworking. In order to skin, youll need to train at a Skinning trainer, buy a Skinning Knife (available from Leatherworking and most Trade Skill merchants), and find yourself something to skin! Of the various mob types, only beasts are skinnable, but not all beasts. Insects and birds are often not skinnable, but most other types of beasts are, so you shouldnt have a problem finding something to take your knife to. You can check whether or not a target is skinnable by mousing over its corpse after it dies.
When you have your skinning ability set up, you can head out into the wilderness and start skinning away. If you obtain your skinning after your character has levelled up a bit, though, you may notice that you cant skin mobs of your level after you kill them; like any profession, youll have to start out on easier targets, which in this case means that youll have to return to a newbie area and find low-level monsters to kill and skin. You should be able to skin anything at level 10 or below with a single point of skinning, but thats just to get you started; to skin higher-level monsters, youll need to have five points in skinning for each level of the mob. For example, if you want to skin a level 30 monster, youll have to have a skinning skill of 150 or higher. As with most collection skills, the difficulty of the collection will impact whether or not youll gain a skill point when you perform it, meaning that youll have to consistently skin enemies near your theoretical limit in order to consistently skill up skinning.
On the good side, though, its very, very easy to skill up skinning, since there are good populations of beasts in every zone; you wont have to hunt down mining veins or keep your eyes peeled for herbs, in other words. If you skin everything thats available to you, you should be able to maximize your skinning skill without having to make "skinning runs" or anything like that, leaving you more time to focus on your leathercrafting.
Tailoring, along with Alchemy and Engineering, is one of the professions that most suits mages and warlocks. With it, you can create cloth clothing, armor, and other items that are most suitable to classes that arent heavily armored. Many of the armor pieces that youre able to create will have inherent bonuses to intellect and spirit, and some will even give you direct bonuses to magical damage or healing, making them recursively useful for spellcasting classes. In addition to the normal armor items, though, youll also be able to make tailored shirts of various colors, odd items of clothing like the Tuxedo Jacket, as well as bags that will often fetch a good price at auction. (If you manage to max out your tailoring skill, youll eventually be able to create bags with up to sixteen slots!)
One of the unique things about tailoring is that, like Enchanting, it doesnt have an associated gathering skill; the raw materials for tailoring (namely, linens of various quality) drop on humanoid enemies throughout the game world. Thus, theres no need to do anything to obtain your materials except adventure as normal, assuming you face off against humanoid enemies fairly often. Unfortunately, the same linens used in tailoring are also used in First Aid, which is available to all classes regardless of their main professions. These means that, when fighting through an instanced dungeon, youll usually have to compete with almost every other member of your party for the cloth drops, unless you all agree beforehand on a fair distribution of them.