Events in CrossEngage are used to track and store user behaviour. No matter what your users are doing on your site, it will almost always be possible to break down this behaviour to events that you can send to CrossEngage
Imagine your website to be a sandy beach and your user being a visitor on that beach. For each step she takes, she will leave a footprint. You as a customer can choose which of these footprints you want to store with CrossEngage, and what information it should contain. There is practically no limit to how many of these footprints you can store for any given user. Please note that once an event has been sent to CrossEngage, it cannot be edited.
Once you have this information available, it is easy to run a campaign on users that walk a certain path on your website, and you can start getting creative!