Hi Nicola, welcome to the community.
No, I don’t think this is a noob question at all. There are several ways you can achieve this, I’m gonna give you one way to do it.
So you have an “Image” column with all the URLs. Create one new column, I assume you want to display it in an image component, let’s call that “Featured”. In the only cell of the featured column put the following formula, assuming you store the images in column A.
=index(A2:A,randbetween(1,counta(A2:A)))
This formula will grab all the rows containing images from cell A2 to the last cell containing data in column A, then randomly pick an index integer, which returns the URL of image in question via the INDEX formula.