What are we supposed to do with these?

Whenever I buy a new bag or some certain material items I find sachets of this "Silica" powder inside. When we were children we were told to "throw it away" because "its poison". Naturally whenever I find them I immediately discard them because they are poison. As a matter of fact I think I am a little scared of them.

But then why would manufacturers go into the habit of placing two sachets of "poison" for us with every purchase? That's ridiculous! There must be a reason why these sachets are included and it is not because they want to kill us by swallowing them!

What are these bags? and how are we supposed to use them? What do you do with them when you find them?