Is it possible to translate without actually editing/revising someone elses translation? How do I do this?
You'll have to look for blue sentences, which haven't already been translated. You can work on some of the newly uploaded documents from the Immersion stream, or upload a brand new one yourself. :)
If a sentence shows as grey or black, then there is no way to translate it without editing or overwriting what is already there.
What Deliciae said. Also, when you're selecting documents to translate you should see an indicator for each document of how much has been translated or checked so far. For me that's visible along the right hand side, but I don't have any experience with any UI except the web one. You can use it to choose documents which still have a lot of sentences left to translate.