Is there a way to see what user made what changes?  

You can do this if you log the changes in the app. There is no built in functionality that logs all changes to the data.

You can either log it in the record by adding a field for LastChangedUser with derivation: current user name and a LastChangedTime with derivation: Current date and one for time: current time or a combined one (datetime). concat(current date,current time)

These fields should be write protected.