Basically, it started with students opposing a tuition fee increase which would have nearly doubled their fees after 5 years, still keeping it lower than the rest of Canada and the US, but far higher than France or Germany which are free afaik.
The student process and negotiations have been in vain, and the whole thing escalated with the police and government trying to intimidate the students into stopping the protests via the usual pepper spray and mass arrests. Then they added special laws to make it harder for students to protest by limiting their rights to protest. They've even done a number of preventative arrests.
All this really did was get a lot of non-students to join in the protest.
At this point, we're reaching record numbers of civil disobedience and of people getting fined for it. It's gotten out of control, and some think come next election the current government will get kicked out or at least become minority.