Class vs instance methods

Class methods belong to the class itself, the blueprint. Instance methods belong to individual instances.

To help me gel these concepts can you guys help me differentiate which level you would assign the following methods to: validatePassword, setCookie, getCookie, findUserById.

At the moment I think they should all be attached to the class because I should be mostly be chaining methods off the class itself. For example my sign-up route handler function starts like this:

models.UserAccount.findOne({ where : { username : req.body.username }})

So it would make sense to add something like UserAccount.setCookie() in the following .then() block

Is that accurate or should most of the emphasis, including the above methods, usually go on the instances