Sometimes it is helpful to know who made a change, or when a change was made. You can view this information by clicking the History link at the bottom of the edit form for a record:
You will then see the complete history for that record like this:
Why can't I view the history for a record?
You need to have supervisor or manager permission and be able to edit a record to view the history for a record. You can learn more about permissions from this help article.