You will obtain the Scavenger Bot in Chapter 5. There will be a quick tutorial on how to use them. Basically you equip it like a weapon (it fills the top slot). There is a scanner. Whenever you get to an area where there are full circles around the middle, you'll know it's a great place to drop the bot to gather resources. You cannot pick up the bot after putting it down. To put it down, aim and fire as if you had a gun. After a certain time limit, it will appear at any work bench you go to. Once you reach a bench, open it to retrieve the resources.