These are the items that can be used in Baldi's Basics in Education and Learning. These items have certain properties that will help the Player progress through the school and collect all of the notebooks for the Player's friend.
Click on the left mouse button to obtain the item. Scroll the mouse wheel (or press the 1, 2, and 3 button) to select the item in the inventory HUD, then click on the right mouse button to use the selected items. That's how everyone use items.
Some of these items are helpful for when you have 6/7 notebooks so use them wisely.