Welcome to the Translator group.You will notice on Translation_Workflow#Language-specific_guideline_pages that a Team Leader exists for your language. While there is no requirement for you to contact your Team Leader, it would be appreciated if you do so.
I suspect that you will want to try on-line translation first, unless you are very familiar with off-line translation tools. It would be a good idea to read through Tasks_and_Tools, Translate_a_Page and Translation_Workflow before starting work. You will find lots of help linked from those pages, but please ask if there is anything you don't understand. You will notice that Translation_Workflow has a link to a language specific page, where the Team Leader for your language is named. He/She will always help with language-specific questions.
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!