How To Jump is an active item slot item that lets you jump over gaps: by pressing the SPACE key Isaac will jump. The item does not have a recharge.
If you are walking in a direction and use this item, you will jump further.
If you're flying however, then the player would just shoot further in that direction of movement thus making it useful for getting to another room quicker.
- The appearance of the item is certainly a reference to the original Super Mario Bros. cartridge package.