Fridays For Future is a movement started by Great Thunberg. It’s goal is to put pressure on politics to fulfill the Paris agreement.
FFF is doing strikes every Friday, with major events once in a while. Before the Covid pandemic, participant numbers reached millions worldwide. The next big one is today, with events around the globe: fridaysforfuture.org/action-map/map/
In practical terms, a FFF strike is a regular, orderly, peaceful, announced demonstration, free and safe for everyone to participate. If your country supports these citizens rights, of course.