Help Regarding hlsl shaders

float4x4 World;
float4x4 View;float4x4 Projection;

float4 AmbientColor = float4(1, 1, 1, 1);
float AmbientIntensity = 0.1;

struct VertexShaderInput
{
float4 Position : POSITION0;
};

struct VertexShaderOutput
{
float4 Position : POSITION0;
};

VertexShaderOutput VertexShaderFunction(VertexShaderInput input)
{
VertexShaderOutput output;

float4 worldPosition = mul(input.Position, World);
float4 viewPosition = mul(worldPosition, View);
output.Position = mul(viewPosition, Projection);

return output;
}

float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0
{
return AmbientColor * AmbientIntensity;
}

technique Ambient
{
pass Pass1
{
VertexShader = compile vs_2_0 VertexShaderFunction();
PixelShader = compile ps_2_0 PixelShaderFunction();
}
}



i am trying to learn how to use shaders with directx and i found this code over d net

icould not understand the following thingsin above code

float4 Position : (POSITION0)?;

float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 ?

Also how these function works
technique Ambient
{
pass Pass1(wt is this)
{
VertexShader = compile vs_2_0 VertexShaderFunction();
PixelShader = compile ps_2_0 PixelShaderFunction();
}
}

Also, let me know if there is any video tutorial on shaders with directx.