The Object Change Log Interface is a default tab on all object forms (to see how to add/remove this tab from an object form see additional help resource). It is used to view all changes made to this object and can also be used to undo changes.
Additionally, for all Contact objects and any object that inherits the Contact, the Object Change Log Interface also records everytime the Contact has logged in and logged out and what IP address they logged in from.
Navigate to the Change Log tab on an object form to access the Object Change Log Interface. When you have opened it you will see a list of every change that has been made to this object; changes to details, permissions and associations.
There are three columns (see image below):
You can view more specific detail about a change by double clicking on the row or by right clicking and then clicking View Details.
You can undo a change by right clicking on the row and clicking Undo. Note, this will only reverse the changes of that entry, it will not revert the object back to the state it was in when that change was made i.e. if you change the name of an object and later change the description, you will have to undo both of those changes seperately. This is because undoing the change to the name will not also undo the change to the description.