underlayment for snap together flooring on slab

ok  so i bought some cheap snap together wood flooring, but i wanted a good underlayment that wood keep the noise down and add a lil warmth to the floor.  I looked at Precision Components premium underlayment. My question is why dose the moisturebarrier go up ? According to the directions on the package . I would of thought that the plastic sheet /moisture barrier would of gone down to the slab . Do i need a second layer one on top and one on bottom ? But to me that still doesn't seem right. Looking for  some insight

If your using a roll of padding that the manufacturer of laminate floor suggest using, go by the instructions. But by no means install two layers.

Yes, as what the previous poster mentioned, do not install two layers. If you’re in doubt, always return to the manufacturer or find a comprehensive instructional booklet. I remember when I bought slip resistant floor plates for my store, and I thought I would be able to install them myself. Unfortunately, it was out of my capability and I ended up paying someone to fix it for me. I don’t have any regrets though. If I had messed it up, it would have been more expensive to have someone clean up my mess and fix it.