To start making money from Flax you will need a crafting skill of 10 (only takes about 5 minutes to get) and you will need to be a paying member.
Head south of Camelot castle to the Flax fields there and just pick Flax there. Pick up Flax until you get a full inventory. Now go northwest to a house there and go up to the second floor, where you will see a spinning wheel.
Now you can make all the Flax intro Bowstrings. You can also buy Flax and make Bowstrings for a profit if you want. A bowstring is worth around 150 gold and you can make a full inventory in a few minutes. So you can make 100k + an hour doing this.
Learn to make Billions of Runescape Gold :