All you need is two pieces of printer paper for the paper star, and a piece of sheet metal roughly 12 cm by 12 cm for the metal star. For tools all you need is a pair of scissors, a hacksaw, a vise and a file. Make sure to wear safety glasses when cutting or filing the metal star, or whenever you find yourself cutting, grinding or hammering metal.
Step 1: Cutting the Paper Into Squares
Let's start with the paper star. The two pieces of paper must be square in shape, not rectangular. To make the paper square simply fold the top right corner of the paper down and to the left so the corner and the adjacent side fit along the left side of the paper. Then fold the rectangle flap that is left over up and behind so you create a triangle. Make a crease at this fold and cut along the crease. The result should be a perfect square. Do this for both pieces.
Step 2: First Folds
Start by folding the paper squares in half. Make sure you fold them in the direction of the arrows in the picture. The openings of the papers should be facing away from each other as shown in the second picture. This will be extremely important later. Then fold them in half in the same direction a second time.
Step 3: More Folding
Next you need to fold each paper downwards in the direction of the arrows. You are making a crease as shown in the second picture. After you make the crease, fold the bottom half of each paper along the crease in the direction of the arrows in the third picture. They should be opposite to each other. After this fold the top half in the direction of the arrows in the fourth picture.
Step 4: Finishing Each Half
Turn the papers upside down from the last step as shown in the first picture. Fold the corners of the square ends of each paper inward to create a shape that sort of looks like two triangles stuck together. Next fold the outside corners inward to make parallelograms.
Step 5: Putting the Halves Together
From this point on I will refer to the halves as X and Y, with X being on the left side and Y being on the right side according to the first picture. This step is fairly tricky and may take a few attempts. Start by folding up the outside corners of the parallelograms as shown in the first picture. Take half X and locate the side that has the flap shown in pictures 3 and 4. You are going to flip this half upside down and put it on top of half Y in a vertical orientation, making sure the side with the flap is the lower side. It should match the fifth picture. Here's the tricky part. Fit the lower left flap of half Y into the flap you found before in half X. Then fit the upper right flap of half Y behind half X as shown in the seventh picture. Flip the whole thing upside down. There should be one horizontal insert going across the star. Fit the upper flap, then the lower flap inside this insert. The result should match the last picture.
Step 6: Finished the Paper Star
Congratulations! You have successfully made a paper ninja star! Please note that this can hurt someone if thrown at them so please be careful if you want to practice your ninja skills. For the more determined, I will now include what is probably the simplest way to create a star out of metal.
Step 7: Laying Out the Star
The easiest way to layout a good ninja star would be to trace the paper one you just made onto the sheet metal. Obviously you can create more elaborate and impressive stars using your imagination, but we're trying to stick to simplicity here. Plus this star is very easy to cut out with just a hacksaw.
Step 8: Cutting Out the Metal Star
This step is pretty self explanatory. Put the piece of metal in a vise and start cutting. Once it's cut out you can scrape off the burrs with your file. Make sure you are wearing safety glasses for this step as it is possible for a metal flake to fly into your eye!
Step 9: Polishing the Metal Star
This step is optional. If you are going to be throwing this around outside, this step is not necessary since the star will most likely become dirty anyway. If you are keeping it as a show piece I recommend it. Start by using a coarse grit emery cloth and work your way up to the finish you desire.
Step 10: Finished!
You can now officially say you own a ninja star! With a little practice (actually a lot) you can learn to throw it and become a real ninja. Again do not throw these stars at anyone or anything fragile because they can and will cause damage, especially the metal one. Treat them with respect as if they were weapons. Thanks for reading and best of luck on your future ninja-related endeavours!