Where can I make my own shaders?

I’ve been playing around with this a lot but every Minecraft shader I’ve come across has either not worked or it has just been bad and I’ve started getting really tired of that.

So I was wondering, thinking if there was any sort of app where you can make your own Minecraft shaders (I’m using MCPE) and I don’t want to spend a lot of money on it so if there is any free app or a website where you can make shaders that would be great.

Any tips?