Gutters are a necessity in print products so that important text or images are not cut off in when the product is printed. There must be at least a 1cm gap around all edges to make sure that it doesn't happen. To do this, I had to add guides which measured 1cm around all edges. I added additional guides for panel lengths as I am making my front, back and spine in as one document.
To make a new guide, I had to go to:
View > New Guide
I then selected which orientation I wanted the guide to be and the distance it measured on the rulers, which I obtained by pressing Ctrl+R.