what does {% set order = 'pin desc, postDate desc' %} do? I am new to using twig and I do not understand how this line of code works. If you could explain that would be wonderful! thanks:)
Craft uses the the template engine twig and there is a set tag that is the same as it's php equivalent for $order = 'pin...'

So you just set/declare a variable - in this case you set the string.