Health

If anybody ever used clearblue digital ovulation test can u please explain to me how it works? They said if u get a solid smiley face it means u are fertile and if u don't get a smiley face that day you are not fertile I just need help because what if i do get a smiley face the day I buy it and what day are u supposed to take the test if anybody knows can u try to explain to me thank u?