I didn't look through those links posted but they're probably a more correct way of doing it than I did. But here's how I did mine on my last quilt;
I didn't have a certain size that I knew I wanted them to be so I just cut squares the same size as the ones I had used to make my pinwheels. I ironed one prairie point and measured how long it's bottom side was. I think it was like 2 inches. I deducted a little for the overlapping I knew they would do, then I divided the length of my quilt sides by that number (the size of one prairie point). I ended up needing a few more but that was no biggie.
When I pinned them to my quilt I had to reposition them a little as I got to the end of each side so the spacing would be even. I sewed them on (facing towards the middle of my quilt) with about a 1/8" seam just to hold them in place while I put the second border on. Ironed them facing out with the second border and I was good to go!
I've read through the procedure of placing them along the edge of a quilt, but I haven't done it.
I think they are one of those great things in quilting that look way more complicated than they actually are. :)