Ok, I'm assuming that you have finished the non-member quest Rune Mysteries
. If not, the link provided has an easy step-by-step manual for the quest. It's really easy and short quest. Anyway, as I was saying, you need to get your hands on at least 27 pieces of pure
essence. If you want to, you can get more just in case. After this, go on either world 66 or 99 on RuneScape. Notice these are so called "law running" worlds. So, go to Draynor bank, and take off any weapons and armor that you have on. Put them in the bank, and take out you pure essence.