gaussianKernel returns a vector but should return a value. #1

Some issues or things I was not able to understand

1. gaussianKernel returns a vector but should return a value.
2. where is the norm function and what it does? (normalization)
3. how this norm(x1 - x2) ^ 2 works? should it be norm(x1 - x2) .^ 2 ?