You need to start with one of my templates. I'll be using the Sudoku page as an example.
The template is double-sided and you need to print on both sides of the paper. With a duplex printer, set it to flip on the short edge. Here's how this looks in my printer's dialog; yours may vary somewhat:
Once your page has printed, place it on a cutting mat to protect your desk. Turn it the right way up so you can see the crop marks, indicated in this picture:
Those crop marks indicate where you need to cut. You need to cut with a sharp craft knife and you need to use a steel ruler to guide your cuts.
I normally start with the rightmost cut. Here's the ruler in position:
Zooming in, you can see how the ruler in placed right at the crop line:
You need to use the knife now and cut from one crop mark to the next. Don't cut right to the edges of the paper, though, just to the crop mark, or a little beyond it:
If you cut right to the edge you will lose the remaining marks that you need to position the ruler for other cuts.
When you've made all three vertical cuts, the sheet will look like this:
You now need to turn the piece around and position the ruler for the horizontal cuts:
When you're all done, you'll have liberated two pages and have the A4 frame left, all in one piece:
You can now punch and file these pages.