gorm如何确定要使用哪个表？

I want connect to SQL SERVER using gorm. I've read documentation how to create new record in table. There is a code:

user := User{Name: "Jinzhu", Age: 18, Birthday: time.Now()}

db.NewRecord(user) // => returns `true` as primary key is blank

db.Create(&user)

db.NewRecord(user) // => return `false` after `user` created

I do not understand, how gorm indicate which table is inserting current record? By struct field or what?