When you click your stock you will be given 2 main areas:
- Salvage - On the right side will be the salvage container which will show all salvageable items currently in your backpack. Salvaging items will earn you resources which are shown on the left.
- Stock - on the left you can see all the resources you have in your camp, which can be used for building camp buildings, research projects, crafting weapons/food, etc. You can also transfer resources to / from your backpack by opening up your backpack's crafting area and clicking the resource you wish to transfer. If you wish to delete resources from your stock, make sure to close your backpack's crafting menu (do this by closing / reopening your backpack).
All resources have their own "max stack" amount, which you can find on their respective wiki pages.