Shaders are not officially supported by Minecraft Bedrock Edition. You have to follow unofficial methods to be able to use these shaders.

Android

1. Install Patch APK

Download and install the Minecraft (Patched) APK.

Minecraft (Patched) APK

The Patch App is a modified Minecraft app with patch to make the game load RenderDragon shader files from resource packs.

2. Install Shader

Download the shader and import it into Minecraft (Patched).

Activate the shader in global resources.

Now restart Minecraft to see changes.

Windows

1. Install BRD

Download BetterRenderDragon.zip and extract it.

BetterRenderDragon

BetterRenderDragon is a mod that lets you enable deferred rendering, disable ray tracing, and load RenderDragon shaders from resource packs

2. Install Shader

Download the shader and import it into Minecraft.

Run the batch script LaunchMinecraft.bat present inside BetterRenderDragon folder. This will launch Minecraft.

Press F6 to open BetterRenderDragon window and then enable the MaterialBinLoader option.

Activate the shader in Global Resource Packs and restart Minecraft.

iOS

No safe installation method for iOS yet. You need to have jailbreak, or use modified IPA as of now.