Press "B" or the Backpack icon to open the backpack. Double click on the tools inside the backpack,then you can use them.
For speedy use, drag the tool in the backpack to the "Action bar", then you can just click to use it.
Note: Certain usage terms are applied to tools. For example, Pet Provisions cannot be used during a battle.
To use collection tools, you first need to be be in the collection area (each map has one of these) but remember that the material you can gather is not the same (where to find materials).
You buy collection tools at a Grocery Store Owner (use Find to search for the nearest one).