I'm new to this game and I can't understand how sometimes I'm able to do it and other times not, even when I've done the glitch, I've seen videos where they only hold the jump button and it works, and when I go to try it I die. Im just a noob so probably It's an estupid question but I dont know what Im doing wrong

You can activate the glitch by pausing and unpausing at any point,so press the p button twice,but you need a high enough speed for it to work,if red ball is too slow,the glitch won't work. Hope this helps :)

also play in 1080p, it makes it more consistent