ArcSite is a subscription based app and requires that you choose and commit to purchasing a specific subscription level as part of the initial use / sign up process.
However Apple allows us to provide a free 14 day trial that starts when you finalize the sign up process. This allows you to try it out and decide if it is worth paying for before you actually do.
As long as you unsubscribe prior to the end of the 14 day trial, you can cancel at any point and not be charged. Here is Apple’s own help article on unsubscribing from a subscription based app.
Note – The free trial is for 14 consecutive days immediately following registration, not the first time you use the app.