Category not being selected

Question

The cat parameter takes an ID and not the category name or slug. If you want to use the slug you need category_name but it must be the slug.

$first_query = new WP_Query('category_name=postblok');

Other category parameters are:

    cat (int) - use category id.
    category_name (string) - use category slug (NOT name).
    category__and (array) - use category id.
    category__in (array) - use category id.
    category__not_in (array) - use category id.