Storage is a trick that gives Link a significantly smaller hitbox and hence allows Link to roll up very steep slopes, walls and even clip through some if the gradient of the slope is correct. Unfortunately due to requiring Map Glitch and a certain type of door, this limits the glitch and currently has no uses.
Firstly perform Map Glitch then enter a door, note that it has to be possible to move around behind the door as some will not have land on the other side and soft-lock you. Once on the inside of the house, have Link hold any item then open the door backwards, the easiest item is just withdrawing your sword however other items can be used such as Ball & Chain as a fun example. Link will now have a very small hitbox and strange collisions that can go up very steep slopes.
This glitch is limited due to the fact Map Glitch disables all loading zones so once in this state you cannot leave through a loading zone, furthermore there are not many doors in the game and not all of them work.
An example of a potential use would be Faron Escape without the boomerang. Storage can be performed using the door to Coro's house and then it is possible to get up onto the wall and around the Midna trigger to the loading zone, however Map Glitch cannot be disabled and the savewarp trigger at this exit doesn't appear to work until after Forest Temple is beaten.
Original video by Zeldagamern01: