node.js - Sequelize - sequelize.sync() -

i don't understand how work istruction sequelize.sync(). example:

into server.js file:

db.sequelize.sync().then(function() {  app.listen(port); console.log("express listen on  port: " + port); }) 

and db.js file create new database:

//create sequelize database export server.js  var sequelize = require('sequelize'); var sequelize = new sequelize(undefined, undefined, undefined, {     'dialect': 'sqlite',     'storage': __dirname + '/data/dev-todo-api.sqlite' // location create new sqlite database  });  var db = {};  db.todo = sequelize.import(__dirname + "/models/todo.js");  db.sequelize = sequelize; //contain settings of database db.sequelize = sequelize;  module.exports = db; 

and __dirname + "/models/todo.js" have created tables/models. server.js when launch db.sequelize.sync(), how know models must stored database? never call db.todo ( create models )

thank morris