wallygator: I can't seem to be able to use inventory items. I'm new to the game and not familiar with the controls.
Hey! Welcome to the island! :)
Not all the items are usable in the inventory - the ones that are are marked with a gear symbol when you scroll through your inventory with your mousewheel (on the left side). If an item is interactable, you can change its state by simply clicking on the moving parts in you inventory view (Q or I button by default).
If you mean: How do I use object from my inventory with the game world? Well, you just have to click where you want to use the currently selected one. No drag-and-drop or anything like that needed. Just select it in inventory view (Q or I) or with your mousewheel, and click on the desired location.
Happy exploring!