You've finished your Project, translated it, then you realize you forgot a Topic, or you want to add a new keyword, or make a change. Whatever changes you make you can track them using Revisions. The initial Revision created with your language is "1.0". If you select "Translations | Revisions" the following screen will appear:-
This shows a list of all the Revisions in your Project on the left. Click on a Revision and the Log will be displayed on the right. The "Notes" tab is for your use. You can add any information which is useful to you in there.
As you can see from the above screen-shot, this log shows no changes for most of the translatable sections, but the Strings section shows that two new Strings have been added since the last Cascade Changes was run. You can print the log using the Print icon at the bottom of the screen.
You cannot add a Revision on this screen. Revisions are added only when you select "Translations | Cascade Changes".