https://www.canada.ca/en/immigration-refugees-citizenship/services/visit-canada.html
there is the link. It's better to apply online since you'll be submitting the requirements one by one so there's less chance of missing a required document.
there are different requirements depending on the country you are applying from, so it's best that you check them on the website.
just to give you an idea, there are online forms that need to be filled-up, you need passports, travel history, proof of financial support, proof of relationshisp, invitation letter, etc. They need to apply individually (1 application per person) but you can submit them in one CIC (citizen and immigration canada) account. You will be required to register for an account in the CIC website.
