This is the finished product

Start with the paper like this

Fold it vertically across the middle

Open it back up

Fold it down the horizontal middle

Open back up

Fold the top left corner down to the bottom right

Open back up and do the same with the other corner

Open it up again, then take in the sides towards the middle

Press down to form a triangle. This is the base, so make 6 of these

The process of making the module is points and pockets. A point goes into a pocket, so put one tip into another base's pocket

They come together like so

Add another base onto two points. They should alternate, so if one side is a point, the other should be a pocket

Repeat the process with all of the other bases

Here you can see how the points and pockets alternate

Now you have a fully formed origami octahedron!