When am I most likely to get pregnant?

This letter reads:

Dear. Dr. Powell:

I am a 16-year-old girl and through one of my recent courses at school have heard that there are roughly four days in a normal 28- day menstrual cycle (about the time of ovulation) when there is a higher risk of pregnancy. Is this information correct and if so does this indicate that pregnancy does not occur at any other time during the menstrual cycle?

I would also appreciate any comments on the complications and risks involved with the IUD.