Runescape is one of the most popular MMORPGs(Massively Multiplayer Online Role Playing Games). It has lots of fun and exciting things to do such as training your skill levels, PK-ing(Player Killing) and lots of minigames to play.
Lots of people have a main account and little "pure" accounts which are generally lower level and made for PK-ing. Pure accounts are accounts which have only been trained in one or 2 forms of combat such as magic and melee, ranged and magic, melee and range or just one form on its own. Pures also usually have a defence lvl of 10 or below.
Melee is physical fighting such as using a sword or a scimitar. This is generally a choice for pures as
when you have a good strength and attack lvl pking is extremely good fun! 
Melee is also good when starting runescape as it is the easiest to train,
it just takes time as all the styles of fighting do. The weapons used in melee can be made using the smithing skill EXCEPT for dragon and barrows weapons,
this is the same with armour. If you have no experience of runescape then this is definately the best choice for starting out!
Ranged Combat is using a bow or crossbow along with arrows or bolts. This is the hardest skill to train by a long way but when high enough it is deadly.

Pures generally don't use range as it takes quite a long time to get high enough to PK but if you have a lot of spare time and are willing to put
a lot of effort in then this may be the option.
Magical Combat is as the name suggests, using spells and staffs. To cast a spell you will need different types of runes, so
this is quite an expensive option but when you get to a high level and have ancient magicks this is extremely powerful. 
Although
using the feared "Ice Barrage" from the ancient magic spell guide costs around 2k per spell cast! This is used by some pures but
almost always used in conjunction with ranged, this is fairly easy to train as long as you have money!
They are the the only forms of combat in runescape but there are LOTS more non-combat related skills, and Jagex are always bringing out new skills such as the recent hunter skill and construction skill.
Armour, obviously... is for protection from other monsters and PK-ers. There are lots and lots of different types of armour which all give different stats and also need different levels to wear. Some armour boosts the defence stats and some boost other stats such as prayer or strength. You must always wear the right armour to fit your combat style though as some armour drains other combat attack stats e.g. If you wore full rune and you was a ranger the full rune would decrease the range attack bonus, but if you wore a range armour such as black dragonhide or Karil's that would boost your range attack bonus.
Weapons vary from swords and scimitars to crossbows and staffs. Usually when people refer to weapons they mean melee weapons but the definition of a weapon in runescape is anything that you can fight with. You will need either a high range level to wield bows or crossbows, a high attack and/or strength lvl to wield weapons, or a high magic lvl to cast spells. Weapons can be player-made using the smithing skill or bought from people or shops. Some monsters also drop weapons and armour such as the abbysal demon who drops the abbysal whip which is currently worth 2-3 million gp in runescape money!
There are lots of money-making guides on the web but nearly all of them are just guides on how to merchant properly...
The only real way to find out how to make money for YOU is to experiment with different types of money-making. 
For instance you
might like to pk for your money or maybe you like to do a bit of farming or make some potions, everybody varies from what they like
to do most. When you come across a good way to make money try to put as much effort into it as you can as some methods in runescape only
last for a few days as everybody finds out and the industry goes bust!
To keep your account safe there are not many things you have to DO but lots and lots of things that you should NOT do, here is a list of some things you should and should not do: