To add HLSL code, you can use the HLSLPROGRAM directive.
Shader "Examples/ExampleShader"
{
    SubShader
    {
        Pass
        {                
              Name "ExamplePassName"
              Tags { "LightMode" = "ExampleLightModeTagValue" }
              // ShaderLab commands to set the render state go here
              HLSLPROGRAM
                // HLSL shader code goes here
              ENDHLSL
        }
    }
}