Shortly after signup, you should receive a confirmation e-mail containing an activation link. Click it to activate your account. Request another one if you did not receive the e-mail within a few minutes.
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.
Investigate and report possible security issues, and help solve them before users are affected. Please don't do this on Framasoft's infrastructure but through installing the projects yourself.