Ohai JigglyZelda =)
Diagonal Love Jumps can be performed out of an attack or throw. Unless you use it all the time in a match, they can be really surprising and catch your opponent off guard. They can also be used to escape certain throws that lead to set ups. The timing is tricky though. You can escape throws like Pika's f-throw and Mk's d-throw, which can both have follow-up moves to hit you with.
To perform the Diagonal Love Jump, you have to jump + hit B as soon as your opponent throws or attacks you. it actually helps me to do this a liiiiiitle bit before they finish this, kind of like with DI where we try to do it in advance. So yeah the jump + hit b is the jumping part, but the direction you move in is dependent on the direction you tilt your control stick, but remember to tilt it lightly. If you mash down on the control stick, you may end up using Farore's Wind, Din's Fire, or Transform by accident lol.
So if you want to tilt it diagonally, tilt the control stick lightly to the side (either left or right) while jumping + hitting b. I hope this helps and I hope I didn't confuse you too much. I suck at explaining things xD