Transifex is a collaborative translation platform. You need an account to be able to contribute to the translations.
Depending of the role you’ve been assigned you can translate, revise, invite new contributors, etc.
Their documentation on how to use the web editor is short but very complete. You should take a look to familiarise with the platform and all its advantages.
If there’s a sentence that you are not sure how to translate, or the meaning is unclear, use the comments and issues tool. We don’t have enough experience yet to define when to create an issue or a comment, so feel free to experiment.
You can also download one or more files to translate them offline or from your favourite tool (some specified below). However, be aware that you won’t see if someone is translating these files at the same time nor use the other tools that Transifex offers. These and other problems that they say in the guide are not going to happen too often if the lesson files are distributed between the translators.
POEDIT is a multi-platform desktop software. It has support to integrate with `Crowdin`_ (a platform similar to Transifex). One of the advantages of using a software locally is that you can see some metadata that Transifex is not showing (e.g., comments made by the po4gitbook tool), however, comments you add in the file are not uploaded to the platform.
OmegaT is a very powerful open source desktop application, it runs over different OSs and understand more than 30 file formats. It has many features and tools, for example it can interact with Google Translate, has support for right-to-left languages and much more.