I explain there how to achieve the spiral effect. I totally get it that it can be a bit confusing when there are no pictures to illustrate the process.
So, let me try again to explain step-by-step how to create a balloon arch or column with a two colour spiral pattern. There's a video at the end which demonstrates the technique nicely.
Let's say you want to create an arch in red and white as shown in the image that I uploaded.
Step 1: Inflate 2 red balloons and tie them into a duplet. Inflate 2 white balloons and tie them into a duplet.
Repeat step 1 until you have blown up enough duplets for your arch or column.
Step 2: Take one red and one white duplet and twist them into a quad. You should now have a cluster of four balloons, where two red balloons and two white balloons are next to each other.
Repeat step 2 until you have enough quads for your arch or column.
Step 3: Place your first balloon quad on your arch frame or line. Twist one of the balloons around its neighbour so that the quad is fixed to the frame. The four balloons should be alternating in colour, that means you have one red - one white - one red - one white balloon.
Step 4: Place your second balloon quad on top of the first one. Rotate the second quad clockwise by about half a balloon. Now your same colour balloons from the first and second quad sit at an angle to each other.
Repeat step 4 for each cluster, always rotating your clusters in the same direction to keep the spiral pattern going.
I am sorry that I don't have images to go along with the verbal explanation.
But I do have a video that should make the instructions clearer, I hope.
The video will start directly at the most relevant part, showing how to arrange the balloon quads to achieve a neat spiral pattern.