TL;DR : unions, high participation, nationwide event
So, usually, protests are called nationwide by unions, and supported by NGOs and political parties (sometimes the other way around, very rarely by the citizen themselves because we have little coordination as individuals, the only time it happened was something big like the yellow vests).
It happens either on the weekend for a protest, or a weekday for a strike, both involves walking down a pre agreed path (usually the main streets of any city where the protest is happening), and ends in a plaza where statements are made. The procession is made up of multiple groups of participating organisations, plus anyone who wants to join. Slogans are sung, people hold signs, flyers are given out, there's batucadas... It's all very fun and invigorating tbh.
Then, in major cities, once the protest nears its end, you may see black blocks forming, also some rioters and looters depending on the thematics of the protest,, and police (CRS) starting to pressure people, by this point it can go south and police may start to block some street access shoot with rubber balls, gas, hit people with their tonfas, make arrests... you name it.
The following days unions will release the number of participants, police will then release their own data, and the real number will probably be halfway between the two claims
Some technicalities: in complete disregard of international law, France gas a requirement where you have to declare the protest and have it approved by the mayor's office two days in advance, otherwise it will be considered "illegal" and police will be violent faster
Most importantly: why does protesting work in France ? Because french people are rarely satisfied, very critical of their government, and complain a lot, but they don't stop there. When we protest, we don't half ass it, we do it in big numbers, it's cultural, and we carry this revolutionary spirit, and we're not afraid to go out in the streets if something doesn't sit right with us.
There's a lot more that can be said about the history of unions in France, and how union culture and "rapport de force" helped protect workers, and how owners have tried to lessen the power of unions leading to less protests, and less workers rights, but I don't feel confident and knowledgeable enough on this subject.
Here are some interesting articles on the subject:
- https://www.syndicat-magistrature.fr/toutes-nos-publications/nos-guides-et-livrets/2664-le-guide-du-manifestant-arrete-mis-a-jour/
- https://www.amnesty.org/fr/what-we-do/freedom-of-expression/protest/
- https://www.slate.fr/story/29471/francais-font-tout-le-temps-greve-manifestation
- https://www.radiofrance.fr/franceculture/manifestations-greves-des-specialites-francaises-1231784
- https://solidaires.org/connaitre-ses-droits/fiche-droits/en-cours-dactualisation/guide-des-manifestant-es-solidaires/
- https://www.gauchemip.org/spip.php?article1093
- https://droit.cairn.info/revue-pouvoirs-2006-1-page-19?lang=fr