Hey House...Been working with the Arduino for a while now. I took a look at the link you provided. It appears you are trying to use the SSR-240A25 model of this SSR. I took a look at the
spec sheet and noticed that the specific model you are looking at requires an input voltage of 90-280VAC. This is what the 'A' stands for in the part number.
Check out the spec sheet I linked above..you will notice on the second page of the PDF that you want the D version of the SSR which provides an input voltage of 3-32 VDC. I am guessing that would be the SSR-240D25. Make sure you spend 5-10 minutes checking out that spec sheet as that will make or break your project.
With an input voltage of 3-32VDC, you should be able to plug this guy in to whichever pin and ground on the arduino and get results. Hope that helps.