An item with just a name isn't all that exciting. This is where item components come into play. Note that these item components should not be confused with item stack components, which are already present in vanilla, even if they might appear to be very similar. Item components go on the item, whereas item stack components go on an item stack.
Item components are what modify the behaviour of an item. They decide what happens when you use an item, or when you break a block with it. Sometimes multiple item components can be combined to make more interesting results! For example, one could combine block behaviour and food behaviour to make a more interesting item, such as carrots and potatoes. Alternatively, you could make an item that is both a tool and a weapon! Any combination is possible with item components.
Every single item component has a dedicated page with its uses and format. These pages can be found on the left in the sidebar, or they can be searched for, much like every other page.