better explanation which exists

In both Ocarina of Time, and Majora's Mask, there is a table of data called the "entrance table". Each row in the entrance table is an "entrance". Each entrance is a little bit of data describing a spawn location for Link, most importantly including a "Scene", which could also be called a "map".

So, for example: "Lake Hylia" is a scene. "Death Mountain" is a scene. "Lake Hylia from the fishing pond" is an entrance. "Death Mountain from Dodongo's Cavern" is an entrance. All of the game's entrances are stored in the entrance table, and referred to by their index in that table, which is called an "entrance index".

Now, let's talk about Majora's Mask's grotto SRM first, since it's simpler (grotto SRM is also a thing in OoT, and it's the same). The code for grottos in Majora's Mask has an array of data in it, and this array contains all of the entrance indexes where grottos can spawn you. Each grotto references that array of entrance indexes to know which entrance to send Link to. With SRM, that array of entrance indexes can be modified. This means that instead of a grotto sending Link to the original entrance, it will send Link to the modified one!

Now, let's talk about Ocarina of Time's glitched Farore's Wind. When Farore's Wind is set, it remembers a few pieces of data about where to return Link to, including an entrance index, a room number, and coordinates (a room is a section of a scene which can be loaded or unloaded. For example, the Compass room in Deku Tree and the Slingshot room in Deku Tree are two different rooms in the same scene). Using SRM, it is possible to edit that entrance index in the Farore's Wind data. On its own, this already means that FW can be edited to take Link to any entrance, but it gets better:

The entrance table only has finitely many valid entries. So, with a sufficiently large entrance index, the game would try to reference data beyond the end of the entrance table, and interpret the data there as an entrance. That data could be anything. As it turns out, there's a certain large entrance index that makes it so that the data that gets read as the entrance, is Link's angle around the vertical axis (Link's facing angle). So, Link's facing angle, since it is being interpreted as the entrance, determines the scene that Link will spawn in! The best part of it all, is that the entrance index can be stored back into Farore's Wind again and again, as long as it is never overwritten without being stored. So, you can warp to any scene, based off of Link's angle, repeatedly!

Additional notes:

-Why does the glitched FW only work as child, and only at night?
Well, OoT uses a pattern of having four repeated versions of each entrance in the entrance table, one each for child day, child night, adult day, and adult night. The game takes the "base" entrance index and adds an additional value of 0, 1, 2, or 3, to reach an adjusted entrance index based off Link's age and time of day. The "child night" version of the glitched Farore's Wind entrance index is the one which aligns with Link's facing angle.