Okay every detail for you. First of all, WoW > Runescape in all ways. World of Warcraft is an MMORPG which is a Massive Multi Online Role Playing.
The adventure begins when you buy it. The total cost of buying the whole thing is about $100 and tax (20 for the original WoW, 40 for BC which is the Expansion, and 40 for WotLK which is the 2nd expansion). To add to that is the $15 a month you need to pay. I guess you don't have to spend anything if you get all of it illegally, which Blizzard will track and hunt you down for. After installing the CDs (a total of 10, 5 for Original WoW, 4 for BC, and 1 for WoTLK) you have to Install A LOT of patches which will take a long time depending on your computer and connection.
Once you have everything installed you log on and choose the server you want to play on. There are a few types, PvE, PvP, RP, RPPVP. PvE servers are regular realms, you have a choice to PvP. In a PvP server, PvP will get to you whether you like it or not unless you hide in cities. RP is for crazy people where you have to always play as if you were your character in the game. RPPVP I guess is the mixture of RP and PVP.
Once you choose your realm, you choose your Faction. There are the Horde and there are Alliance. You choose. Just advice though Horde is way better than Alliance. Alliance is full of little kids. Once you choose your faction, you choose your race. In the Horde, you have the Orcs, Trolls, Undead, Blood Elves, and Tauren. In the Alliance you have the Humans, Dwarves, Gnomes, Draeneis, and Night Elves. Each race has a different racial skill/passives (in-born abilities that are unique to that race only). Once you choose your race you choose your class. There are 10 classes (Warrior, Paladin, Rogue, Shaman, Priest, Warlock, Mage, Hunter, Druid, and with the new expansion the Hero Class the Death Knight). Each class is different and comes with its unique arsenal of skills, read online or the manual to see what they are. You pick your class from these 9 (The Death Knight comes later when you reach level 55 on your original character). You pick a name then you enter the world.
Your adventure now beings. You start at level one. You must now get to level 80. You get there by doing quests or killing monsters, or both. Quests are given to you by Quest Givers and you complete their objectives. You get experience from completing quests and monsters that are around your level range.
You choose your professions too (for example mining, tailoring) which you level up in order to make money in the future. Read online to see what all of these do. You can only choose 2 of all the main professions to keep. The secondary professions can be learned altogether.
Starting at level 8 you can enter a Dungeon/Instance. These are areas where you zone in through a portal into the special Dungeon while you are in a group. Zoning in through the portal will create a copy ONLY FOR YOUR GROUP In these you group with at most 4 people, altogether a group of 5. In here you kill special monsters with higher and better loot and better gear. These are where bosses at. In instances you have special jobs depending on what you want to do. 1 person is usually the tank (A warrior, a druid, or paladin...and later a Death knight) who makes sure the monsters attacks nobody but the tank. A healer who keeps everyone alive. And the 3 DPS who do damage to the monsters.
At 60 there are raids..but they are obsolete. Level 60 raids were in the Original WoW and consisted of having 40 people working together to kill hard bosses. Burning Crusade at level 70 raiding required 25 people or 10 people. Wrath of the lich King now at 80 has 10 people or 25 people working together. Each raid is different and has different boss fights. They take skill, coordination, and some Redbull to keep you on your feet on your computer. It takes execution to pull off these raids.
Patches arrive and bring new additions to World of Warcraft.
The forums online are where you can discuss many things (Suggestions, questions, problems).
Guilds are for you to join and meet new people and raid with.
You can either PvP (Player VS Player) or PvE (Player VS Environment) or both.
PvP is where Player vs Player happens. You can either do World PvP, which is going outside and killing people of the opposite faction. Or you can go to battlegrounds where you fight people with a special goal to complete in order to win a game. Or you can Arena (different types of games for different # teams. There's 2v2 [Your team of 2 versus a team of 2], 3v3, 5v5). These rated matches are serious business to people.
When you Arena or do battlegrounds you get better gear with resilience in it. Resilience is for PvP and all it does really is decrease the damage other people do to you.
When you raid you get more cool looking gear and weapons to show off. When you raid and you're good at it you can stroke your E-peen in major cities.
The impact you make on those around you in this game will make you either famous or just a regular Joe in WoW.
From a WoW player to a Non-WoW Player, it is really fun....but really addicting. Overall, don't play this game if you're young. It'll ruin your education.