passwords – How can I use a unique salt for each user

I know there are various questions that seem similar, for instance, this one. However, it does not answer my question.

I’m creating a signup/login system (with node.js to be particular), and I’m trying to hash the user’s password (with bcrypt), as well as use aes-256 for the rest of the user information. I’ve been told that I should use a different salt for each user.

My problem is when a user creates an account, his password is hashed with a special salt and stored inside a database along with other user information. When the user logs in, I hash this password with the salt I assigned it when he signed up. However, how do I know which salt to use out of all the salts in my database?

There’s also this option out there (comparing a plain text to a hash):

bcrypt.compare(myPlaintextPassword, hash, function(err, result) {
    // result == true
});

But how do I know which hash (of all the other hashes in the database) to compare to the user input? Also, if bcrypt could check if it matches without a salt, couldn’t anyone do that?

I believe there must be a better implementation of this… is there?