How to use shader?

I have pixel shader and I want to use it on camera but I have no idea how to put in it.
I already create a new shader and put the code in it. I try to drag it on my camera but it doesn’t work.

    Shader "Pixelate" {
        Properties {
            _CellSize ("Cell Size", Vector) = (0.02, 0.02, 0, 0)
        }
        SubShader {
            Tags { "RenderType"="Opaque" }
            LOD 200
           
            GrabPass { "_PixelationGrabTexture"}
           
            Pass {
                CGPROGRAM
                    #pragma vertex vert
                    #pragma fragment frag
                    #include "UnityCG.cginc"
               
                    struct v2f {
                        float4 pos : SV_POSITION;
                        float4 grabUV : TEXCOORD0;
                    };
                   
                    float4 _CellSize;
                   
                    v2f vert(appdata_base v) {
                        v2f o;
                        o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                        o.grabUV = ComputeGrabScreenPos(o.pos);
                        return o;
                    }
               
                    sampler2D _PixelationGrabTexture;
               
                    float4 frag(v2f IN) : COLOR {
                        float2 steppedUV = IN.grabUV.xy/IN.grabUV.w;
                        steppedUV /= _CellSize.xy;
                        steppedUV = round(steppedUV);
                        steppedUV *= _CellSize.xy;
                        return tex2D(_PixelationGrabTexture, steppedUV);
                    }
                ENDCG
            }
        }
    }

[SOLVED]
Make a new cube. Attach infront of camera. Put a new material in a cube. Select from “Diffuse” to “Pixelate”. Done.