Now that the Paris Agreement has been adopted and signed, what has to happen next for it to serve its function in, you know, saving the world? Here’s a quick recap of what happened last Friday at the massive United Nations event, and a look at what will happen now that the global community has shaken hands and agreed it’s time to take global warming seriously.

First the agreement has to clear the final hurdle in the three-step process—adoption, signing, ratification—to officially go into force, At that point it will officially be in the United Nations’ books and certain parts of it will be legally binding. To make that happen, parties have to clear the 55-55 test. That is, at least 55 countries that together account for at least 55-percent of global greenhouse gas emissions have to go through the legal, executive and legislative hoops back home so that they may formally accept or ratify the agreement.

As soon as these thresholds are met, the Paris Agreement kicks in for real. On Friday, 15 countries jumpstarted this final process by submitting their formal “instruments of ratification” to the U.N. A bunch of others—including some big polluters like the U.S., China, Canada and Australia—have said that they’ll join as early as this year. According to the World Resources Institute’s handy Paris Agreement Tracker, the 25 countries that either joined Friday or say they will early gets us within 10-percent of the emissions threshold.