Formal:
* Bonjour à tous, aujourd'hui je vais vous parler de la France. (This is the most formal option, suitable for a classroom or professional setting.)
Informal:
* Salut tout le monde, aujourd'hui on va parler de la France. (This is a more casual option, good for a group of friends or students.)
* Coucou tout le monde, on va apprendre sur la France aujourd'hui! (This is a very friendly and informal option, often used with children.)
You can also add a little more context to your greeting, such as:
* Bonjour à tous, aujourd'hui, nous allons découvrir la France. (Hello everyone, today we will discover France.)
* Salut tout le monde, aujourd'hui, nous allons apprendre des choses intéressantes sur la France. (Hello everyone, today we will learn interesting things about France.)
Remember to choose the appropriate level of formality based on your audience and the situation.