So let's make some.
First cut 6 inch squares.
If you want a 2.5 inch point, plus a half inch seam allowance you will need folded triangles that stand at 3 inches which means you will need to cut squares that are 6 inches. This is easily done with a rotary cutter. Cut 6 inch strips of your 45 inch wide cotton fabric, then slice those strips into 6 inch chunks (squares).
By the way, you'll get seven six (6) inch squares out of one 45 inch strip of fabric.
Fold diagonally matching the corners of the square, and diagonally again. Pressing as you go. And you get a prairie point.
Now that you have the idea, let's make a project with prairie points:
Because I'm still sewing-by-hand until the machine gets fixed, I've opted for sample size... a ten inch prairie points potholder. Just big enough to show off the prairie points but not big enough to make my whine about the fact that my machine is still at the repair shop.
So how many p. points do you need? Back to the math:
If we use the same size (6" square = 2.5 inch high, finished) for our points, that gives us a placement of roughly one roughly every 3 inches. You could space them out more, but I like mine overlapping. So on my 10.5 inch piece of fabric I'll use 12 p. points. (A 45 inch square baby quilt would require 58-60 p. points this size.)
Arrange your prairie points facing into the center of your "quilt" and pin in place. The way I do it, they are allowed to hang over the edge by 1/4 inch.
Stitch down. (If you're hand stitching, a basting size running stitch is fine.)
Next, layer the back on top, right sides together, and sew leaving an opening. Use a quarter inch seam allowance. (Hand sewers, here I used a running back stitch -- to make it easier to get tight seam through all the layers.)
Once you have it sewn together, trim the bulk away from the corners and flip right side out. Take your batt, cut to the finished size, and insert it. I've used a 10.5 inch square, with .25 inch seams [math: 10.5 - (.25+.25)= 10] so I'll use a 10 inch square of batting. (Actually, because this will be a potholder, I'll use three layers of batt; but quilts only need one layer.)
I use an invisible stitch to close the opening, and then it's ready to quilt. This small size doesn't need to be basted, but a larger quilt would obviously require some basting. Some people also prefer to sew the prairie points to their quilt top, then layer and quilt normally, following which they trim down and hand sew the backing to the stitching line of the p. points. If I ever do a queen size with prairie points I think that method would make sense.