If someone on the street came up to you and asked "How does a the birth control pill work?" what would be your answer? Hopefully better than some of these guys:
As funny as that video is, the sad part is that these are real people giving honest answers on a pretty important topic. To offer a little clarity, and since I try to be informative, even if it is in a mildly inarticulate and slightly awkward way, here are some general descriptions on how a few of the major forms of womens birth control actually work.
The pill - Also known as oral contraceptives. The pill contains hormones that suppress ovulation. You remember that from biology class, right? A mature egg is released from the ovary when the surrounding follicle breaks open in response to a hormonal signal as part of the menstrual cycle. No egg, no fertilization, no pregnancy. Additionally, the pill thickens the cervical mucus to block sperm and keep it from reaching an egg. The pill typically contains progestin and/or estrogen. Progestin keeps the sperm from reaching the egg and prevents implantation, and estrogen stops ovulation.
The morning after pill - This is widely considered as a form of emergency birth control to be used to prevent pregnancy after unprotected sex. Conception rarely occurs immediately after sex but rather after ovulation, which can be days later. During the intervening time, the sperm travel to the fallopian tube(s), where they hope an egg will be traveling on its way from the ovary to the uterus. The hormones in the morning after pill are similar to those in regular birth control pills, only there is more of them. The objective being to prevent fertilization of the egg. Depending on the type you are talking about, they either contain levonorestrel or a combination of progestin and estrogen.
The patch - This is a small patch that sticks to the skin and releases hormones to prevent pregnancy. These hormones are the same as in the birth control pill (progestin and estrogen), and as with the pill they prevent ovulation and thicken cervical mucus.
The NuvaRing - This is a relatively new player in the birth control game. It is a small, flexible ring that contains the same hormones as the pill and is inserted manually into the vagina where it releases a continuous, low dose of these hormones. It is left there for three weeks and then removed for one week for the period.
The diaphragm - A birth control device (no hormones this time) that is made of rubber and is shaped like a dome. It fits inside the vagina and covers the cervix to block sperm from entering the uterus (and beyond) and fertilizing an egg (often used with spermicide).
The intrauterine device (IUD) - This is a small implantable device that is shaped like a "T" that goes into the uterus. There are two types: (1) the copper IUD (ParaGard) which releases a small amount of copper into the uterus that prevents the sperm from reaching the egg and prevents egg implantation into the uterine wall and (2) the hormonal IUD (Mirena) which releases progestin into the uterus that keeps the overies from releasing an egg and causes the cervical mucus to thicken so sperm can't reach the egg. Both types of IUD's can stay implanted for up to or at least 5 years.
Here are a few reliable sources for information about human reproduction and birth control (including many of the methods that I did not list here).
A lecture course from the University of Utah on Human Reproduction
Columbia University Mailman School of Public Health Reproductive Anatomy and Physiology
Office on Women's Health, U.S. Department of Health and Human Services
NIH Eunice Kennedy Shriver National Institute of Child Health and Human Development
Planned Parenthood's Birth Control Page
I would advise anyone to look into the topic before forming an opinion -- Make sure you are reading scientifically reliable sources!