There are no instructions with the Pony light duty Woodworker's Vise, and I couldn't find any information on the web, so I wrote to the manufacturer, and this is what they told me:
The vise should be attached from two directions. The top of the vise should be aligned level with, or just below the top of the workbench.
First, use the two outside holes (with countersink) to attach the face of the back jaw to the front edge of the workbench with wood screws. Then, from underneath, use lag screws to attach back jaw from underneath workbench.
Once the back jaw is attached, align the main screw and rods of the front jaw on to the back jaw.
You also have to remember that if you are going to face the jaws with wood, you need to screw the wood to the backplate before you mount the backplate to your bench. That also means you will have to drill two holes in that wood to allow you to drive the screw heads through the backplate into the bench. You might have some difficulty separating the front and back plates - just extend the jaws as far as possible, then jiggle the main screw a little and it should come out without force.
The lag screws should be 1/4 inch diameter. The wood screws that go through the back jaw will need to be #10.