It means that the sponsor is responsible for you financially for 3 years. You can still work but if you should fall ill or not be able to find a job and you have to go on welfare, your spouse is responsible, even if you had since divorced. There are actually cases of marriage fraud where a foreigner has tricked a Canadian into marrying them but as soon as they have their papers, they leave the person and go on welfare and after that even on disability and the defrauded spouse has to pay the bill. That's the way the system works here, you bring them in, you have to take responsibility for them.
If you apply for outland sponsorship where you are officially not living in Canada yet, it can take from 3 months to a year depending on where you are and you get permanent residency at the end of that period and will then be able to move to Canada and work. If you apply inland where you are already in Canada, you will get a work permit in about 6 months but permanent residency later.
