Welcome to the Translator group, and sorry for the delay - I've been away. You will find helpful advice linked from the Translator Help Pages in the sidebar.
The option to export messages for off-line working is found in the first combibox of the page you reach via the Translate this Page link. When you work off-line we ask you to send your first set of messages to me for uploading. Once it is confirmed that they upload without a problem you will be told how to upload them yourself.
Please ask if you are unsure about anything. Enjoy!