This article explains the most common constraints and what they do: https://community.marketo.com/MarketoArticle?id=kA050000000KzKZCA0
Constraints are typically pretty self explanatory but some of them can be a little confusing if you are not familiar with the terms. I would suggest making a list of the ones you aren’t sure of and I am happy to explain them.
Hi Jeffrey It would be great if you could also explain about the "referrer" constraint. We have an email trigger campaign set up to send an email if a user submits a form on a particular page. We are using the new Marketo 2.0 forms embedded on our own web page. In the smart list > fills out form settings, we have used the "referrer contains.." constraint to tell Marketo which page the form is on, so it knows which email to send. The form works fine without the referrer constraint, but it breaks the program when we add it back in. There doesn't seem to be any info about the referrer contains constraint in the help portal, so am having trouble figuring out if we have configured this correctly.