It's a fairly easy you cut the blades and then if you want a circular edge, leave as is. For points, you fold each blade right sides together at the outside edge and stitch across. trim the corner excess off and turn out. Use a point turner to get the good point. I the use a piece of heat resistant template plastic which has an exact 90 degree angle which I put inside the point and has a 45 degree line marked. I Line that up with the seam line I just sewed. and press.
When stitching the blades together I always work from the outside edge inwards. You are going to cover the base with a circle anyway so I would rather any slips or slides end up down there than on the edge.
Spray starching you fabric before you cut makes the sewing easier. remember you have both edges on some bias so be careful of stretching.
Piece 90 degrees of blades together and then Square it up with your big quilting square before sewing it to the next one. You can just appliqué to a square and use that as the template if doing a single quarter circle. If doing a full plate square them up before sewing them to the next set of blades. That way they should sit flat when you come full circle.
If points you can appliqué the folded edges down by hand or machine. Just pin it carefully to the background square and it is well worth running some large hand basting stitching around the edge to hold it so you can take the pins out.
I did do a small one hand piecing over papers but I prefer to machine piece. I have never got one to be exactly 90 degrees with out some trimming but no one would ever know!
Oh dang it I just told you didn't i :)