Telling Weblate what languages you understand/translate will make it easier afterwards. You can also take a moment to edit your account profile and settings if needed.
The Framasoft GitLab instance is hosted at framagit.org. You have to sign-up here, using your e-mail account or by way of a third-party token provider.
Weblate will now present you with text in need of translation or correction. Confidently submit a translation, or fill-in your proposal and submit the form. If you're not sure at all, comment or move to the next string.
We know writing an actionable bug report is hard. Do your best and give as much context as possible, but don't worry: other contributors will reach out to you if they need more details.