Pubic lice (sometimes known as crabs) are small insects that are normally between 1-3mm long. They are passed between people by physical contact, or via close contact (such as sharing a bed, or a towel). Generally the first signs will be itching around your groin (particularly where you may have pubic hair). For people with facial hair, there are some rare occasions where they will be found there too.
They can normally be spotted with a close examination of any area where there is hair (the lice tend to cling to hairs to stay in place).
Lice themselves do not cause any serious issues, beyond being embarrassing and irritating. However, itching and scratching the area can often break the skin. Treatment of lice is simple - visit your doctor, local pharmacy or drug store and they’ll give you a medicated shampoo or cream, along with other instructions (normally to wash all your clothes and bedding to ensure that they’ve been killed off).