An erection means a stiff penis. A stiff penis is generally between thirteen and fifteen centimetres long, from root to tip. However, some are longer while others are shorter. The size of a non-erect penis does not predict its size when erect.
The penis is composed of three types of spongy tissue. These are soft when the penis is not erect, but when it becomes erect these fill with blood. The veins carrying blood away from the penis close, so that blood is trapped in the penis. This leads to the penis becoming stiff. When it is stiff it often becomes curved; in some men it will curve down, in others upwards or to the side.
Erections usually occur in situations when you are sexually aroused. Young men often get this without having any sexual thoughts or feelings. This is totally normal, and is a result of the body’s hormones being very active in puberty. It is also normal for men to have an erection when they wake up in the morning, especially when they are young. This does not necessarily mean that they want sex or have had a sexual dream.
When the man has an erection his penis can more easily enter the vagina during sexual intercourse.
When women are sexually stimulated, they also get an erection. Then the clitoris and the spongy tissue around the opening of the vagina swells.