Every flower has specific parts and each part has a specific role. The stigma is just one part of the flower and without it, flowers would not be able to reproduce and bear fruit and therefore seeds. They all work together. To understand what the stigma is and how it works, you have to have a general understanding of the other parts of the flower as well.
Look directly into the middle of the flower. You should see a thin stalk (called the style) protruding out from the middle of the flower. On top of the style is the stigma, which is sticky and has the shape of a bulb. The size of the stigma varies from plant to plant and some are easier to see than others. In some flowers, the stigma is hard to see, whereas in flowers like tulips, the stigma is easily seen.
The stigma is just one small part of the female section of the flower called the pistil. The other parts of the pistil are the style and the ovary and ovule, which are found beneath the style. The stigma is supported by the style. The style is connected to the ovary and inside the ovary is the ovule. It is the ovary that will later become the fruit, if it is fertilized, and the ovules inside will become the seeds.
The male section of a flower is called the stamen. It has two smaller parts--the anther and the filament. There are generally several stamens in the flower that are also found shooting up from the center of the flowers like small stalks. They stick up along the sides in a circle, usually surrounding the pistil.
Most flowering plants have both the female and male parts in the same flowers or in separate flowers on the same plant. A few others have either the male or female part and will only reproduce if plants of the opposite sex are nearby. Reproduction occurs when the plant develops fruit with seeds inside that can turn into future plants.
The stigma is sticky. The stamen makes pollen. The pollen is carried naturally by such things as bees, butterflies and the wind and sticks to the stigma. The stigma then sends the pollen to the ovary and to the inside of the ovary where fertilization begins so that the flower can bear fruit. Fruit is not necessarily the fruit we eat, but the part the surrounds the seeds.