The picture on the left illustrates an ovulation cycle. The key stages of an ovulation cycle are as follows:
The follicular phase is shown in blue. It starts at the beginning of the period, and ends when ovulation occurs. This phase typically lasts 11-21 days.
The luteal phase is shown in purple. This phase starts on ovulation, and continues on until the beginning of the next period. The luteal phase averages around 14 days and can range from 12 to 16 days.
The menses period is shown in red. Menses refer to the bleeding associated with the period, and can last around 3 to 7 days.
The fertile period is shown in green. Fertile period is the time period when it is possible to get pregnant from having sexual intercourse. It typically starts from 3 days before ovulation to 2 days after ovulation, for a total of 6 days. The best chance of getting pregnant is on ovulation day. On the other hand, having intercourse during the fertile period does not guarantee pregnancy. In fact, even for healthy couples, the chance of getting pregnant in any given cycle is only about 15%.
The video below walks through the key stages of an ovulation cycle.