From here I am going to let you at it. You don't need me any longer for these steps, but if you get stuck, just review above or on the wreath project and you will start to get the hang of this. There really isn't a right or wrong and everything can be fixed if you make a mistake, which you won't.
From the image above to create 2 additional triangles you simply thread 2 straws and run your string through the straw on the bottom left hand side of the shape. Then, thread one straw and connect the two triangles just like in the previous step. Tie it off to keep it tight and turn it around to the other side and add your two triangles there.
You will essentially repeat the process until you have nothing left but a diamond shape and you will simply need to thread a straw to divide it and tie off.
Below is about where you should be when you add the 2 triangles to each side of the shape from above.