Shield Jumping is an intended game mechanic that enables you to jump further and/or higher than a regular jump would allow.
To perform this technique, use a running jump or a forward hop to get into the air. Then hold target (ZL) and press the action button (A) to make Link jump on his shield to start a shield surf.
Landing on your shield after a shield jump will damage your shield in most cases. Unequipping your shield before landing will prevent this. When using shield jumping to gain height, or to cross far distances, you can unequip your shield before reaching your destination to put Link back into a regular jumping animation, allowing him to climb up ledges. This makes landing some shield jumps much easier.
Note that unequipping your shield during a shield jump will desync Link’s physics tics from the rest of the game world, meaning you must resync your physics tics before performing a Stasis Launch. There are many ways to to this - the easiest of which is to shield jump onto your shield, as if you were doing a shield surf. While Link is standing on the shield, unequip it. Alternatively, you can take damage from an enemy or a remote bomb while in the air. Both of these methods make Link enter ragdoll mode. When he gets up from the ground, his physics tics will be resynced.