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.
Every project can be made up of several subprojects, also known as components in Weblate's terminology. Pick your favourite, or "Contribateliers" to translate this website.
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.