Superslides work by shielding damage at the same time as trying to grab something (usually a bomb). The Superslide is the fastest known method of travel in the game next to HESS, so it's good to know. Although HESS is more common for HESSes of large distance, Superslides are still used in some cases where you only need to go straight. For instance, Hover boots can be equipped after starting a Superslide to hover over large gaps such as the Shadow Temple chasm or across the hands outside Spirit Temple. It's also fast enough to clip through many walls (though HESS is more often used). Navi or owl text triggers can also be skipped in this state. There can be funny side effects while holding a Superslide through cutscenes and allows you to keep the Master Sword in the Ganon cutscene, which is one of its greatest uses. Link won't lose his sword without the scene of him losing it occurs, and with the shield up, Link stays still and Ganon's attack just hits the shield. Link's shield must be held the entire time during a Superslide or it will end.
A Superslide is set up similar to a ground jump; however, the timing is more precise. The easy, automatic way is to cast Nayru's Love, and then set up a Ground Jump. After you are hit by the damage (bomb, enemy, etc.), instead of storing the jump you will do a Superslide.
You can Superslide without Nayru's love:
Hold Z, shield drop a bomb (wait until Link is holding it above his head), and press A to roll forward once, then backflip. Do not instant shield drop the bomb, this will make it more precise, because the bomb is not centered with Link and ends up being considered a distance akin to a step back from the bomb. Alternatively, you can shield drop, backflip, neutral roll forward.
Soon after the bomb's flashing quickens (around 7th red flash), mash A rapidly until you have finished rolling forward. It is a 4-frame window to roll as Adult Link and 3 frames to roll as child. However, child can slide more successfully because he has more frames to grab the bomb.
For Adult, the 2nd roll frame will often be a ground jump because you have to grab the bomb on one 5 frames of Links's roll to slide. You can also only grab on this frame for the 4th roll frame, however, there are no other frames to grab the bomb so it will often slide if you mashed well. This grab frame (with is the 5th frame of Link's neutral roll) will work on all 4 superslide roll frames.
As a sidenote, Child can superslide well with instant shield dro, because his shorter roll puts his distance closer to the bomb than Adult.
With enough practice you can superslide in this manner with a high success rate, though it is only useful to know in limited scenarios, it's good to know. Shadow Temple boss key skip can be done with a Superslide and is often used.
The frame data for Adult slides can be seen here
Each image represents his 4th frame of Link's neutral roll to the 8th frame (which will never work. The first frame to roll is the most lenient, but is followed by the bad frame. It's good to try and get a feel for rolling on the last 2-frames.
With one bomb, the timing is very strict as you have to grab the bomb as it is exploding. By using two bombs, you can shield the explosion of one bomb while grabbing a separate bomb, thus giving you many more frames on which you can successfully get a Superslide.
For a two-bomb Superslide, you can drop the bombs as shown in the video and mash A to roll and grab the second bomb just before the first bomb explodes. It can be done with them dropped left to right or vice versa. The video below how to set up the most common, easy setup, and it also shows how to perform a 2-bomb Superslide while backwalking to cover distance (a more advanced technique that takes practice). It can also be done with 1 bomb, but is a lot more difficult. You have many more frames to grab the 2nd bomb as Adult, and your distance from the bomb is less important.
Here is an in-depth tutorial based on the easy method made by ArthurOuidini which also includes frame data.
As mentioned, Superslides can be done without bombs. You just need another grabbable object and another source of damage. The grabbable object can be bushes, pots, bomb flowers, etc. The damage can be most enemy attacks, ones that don't knock Link over and his shield will block. The trick is to roll forward, and just as Link's about to finish rolling, have the enemy attack him and he will block it with shield. If done correctly, Link blocks the attack and will Superslide. This isn't a commonly used technique, but can be done in Haunted Wasteland to get a recoil Superslide from a Leever (either intentionally or by good chance) while performing a backwalk Superslide.
If the object you are interacting with is something that Link can't lift, such as bomb flowers or grass before you get a strength upgrade, it's possible to do what's called a Superslide Teleport.
To do this, first get a superslide off one of these objects in a similar way as 2-bomb superslides. Note that it must not break in an explosion; the original object must still be intact so you can grab it, so if you use bombs a bombchu be careful be cautious. After getting the Superslide and being shot back, let go of R, and you will be shot back to grab the object. Link will grunt and won't be able to pick it up. Note that if you superslide too far you will no longer be able to teleport back to the object.
The trick is useful however, because of one extra characteristic: When you warp back to the object, the Z position of Link does not change from where he teleported from. This means that if you Superslide up a hill or slope and then warp back, you will be over top of the object you are trying to grab, and if you performed ISG beforehand you will stay there in the air. This used to be useful in some cases such as getting into Shadow Temple Early. That was obsoleted by a Hookshot Jump off Dampé's Hut. Additionally, if you go down a slope and warp back, you will be out of bounds below the object. It can be useful in certain situations as well, especially where there is out of bounds water to swim in.