Hi Star, Welcome to the fcp.co forums
Tom is right, paid software is not transferrable and should have been removed from Mac before it was sold.
However, almost all software on your Mac should be usable. None will be updatable as the purchases are tied to an Apple ID account. So the version(s) is locked until you decide to purchase FCPX outright, in essence a trial version for free with unlimited time to use, or until the first time you need to redownload and re-install the app. This will occur at the most inopportune time.
One issue, if the Mac you bought is not upgradable to the latest OS version, then you may have to jump through hoops to purchase the last version that would work with you Mac. Latest FCPX versions require later OS and will not work will earlier OS,s. Suitable versions are not directly available on the App Store. Tom has posted a method of purchasing older versions of apps.
Best of Luck and have some fun!