A signup bonus (a casino signup bonus, of course) is a bonus that a casino or sportsbook gives you upon registration. There is no need to make a deposit like with “welcome” bonuses, so there is no need to invest any of your own money.
The only hard work is to create an account, and then maybe also submit KYC documents if you win enough or play through the wagering requirements and are ready to withdraw your winnings.
For example, a 200% match up to C$100 means if you deposit C$50, the casino will give you C$100 more to play with.