"View revision history"
To view a file's Revision History, click on the file and then select Revision history from the Action menu. You can also use the View revision history shortcut.

Each entry in the Revision History offers several links:
 

File Content Display
In the Rev column, the revision number is a link to the content of the file at that revision. It's also an entry point to Back-in-Time Browsing®, when applicable. This link is present regardless of filetype, for all non-deleted file revisions. (See Displaying File Content for more browser-related information.)
Diffs To diff between a file revision and its previous revision click the Diff shortcut. This link is available only for text files between non-deleted revisions. You can also use the Diff commands available from the Action menu.
 

Changelist Description
The changelist number is a link to the Changelist Description. This link is present for every revision.

File Text
To view the plain text of the file at that revision, click the View file text shortcut button. This is available for text files at non-deleted revisions only. (See Displaying File Content for more browser-related information.)
 

Browse Files
Files shown as integrations to or from the current file are links to the File view pages for the integrated files.