Ok lets get started.
First of all you need to create a totally new account.
During the tutorial, you need to make sure that you only get your accounts' mage level up as high as it can (level 4).
Now you are ready to become a pure.
If you have a main account, then this process will be a whole lot easier. To become a pure in magic, you need runes. Now here's where the main account comes in handy. You will need to transfer money to your pure so it can purchase runes. The fastest and easiest way to get just your mage up is to get your mage level to 21 and buy a ton of nature runes. Nature runes go from anywhere between 100-400gp from someone who knows what prices are. The reason you need your magic level to 21 is because you will have the ability to low alchemy. To do this you will need to buy a fire staff. Hopefully you didn't spend all your money on nature runes because you will also need to buy something to alchemy. The best thing to alchemy on a f2p (free to play) world is a maple short or longbow. What you need to do is buy as many as these as you have nature runes. The reason for this is because alchemy spells only use one nature rune. After purchasing the items to alchemy, you now need to use the spell on the items. This therefore gets your only your magic level up and not your combat so you will now be set to pk!!!
If you do not have a main account, the best way to make money on a pure is to get its mining and smithing to at least 48 to make full steel and sell it. Another way is to get your woodcutting up to 60, which is pretty easy, and sell the yews that you cut.