The Sacrament Of Reconciliation

All Catholics who have reached the age of discretion (normally about seven years of age) are bound to confess all their grave (mortal) sins, and as soon as possible. In the case of mortal sin, there is an obligation (if the sin has not been confessed as soon as possible after it has been committed) to confess that sin during the period between Ash Wednesday and Trinity Sunday. There is no obligation to confess non-grave (venial) sins, but the Church urges us to do so on a regular basis in order to receive the grace of the Sacrament so as to grow in the love of Jesus Christ. In the case of children, they have to make their confession before receiving their first Holy Communion.

Please read "The Examination of Conscience for Adults"