The contraceptive patch is called Ortho Evra in the US. The patch has the same types of hormone as is found in birth control pills. It just uses a different way of getting it into the body. It is placed on the skin and left on the skin for one week. It is then removed and a new patch is placed. Three weeks of the patch is followed by one week without a patch. This has a failure rate slighter better than the pill as it is easier to remember.
The patch can be placed anywhere on the skin except on the breasts. Most women will place it below the pant line in the front or back. It is recommended to rotate the site to avoid skin irritation. Most women will have three or four places they use on the skin and rotate each week.
There was some bad publicity about the patch a few years ago because of higher failure rates in obese women. This is actually true of any hormonal birth control method. The problem is that these contraceptives have a fixed dose of medicine, so that the effective dose for larger women will be lower than for smaller women. Even so, the failure rate is very low, though not zero, even for larger women.
The advantage of the patch is it only needs to be remembered once per week. The disadvantage is that it is something that must be worn on the skin and can cause skin irritation. Otherwise, it has the same side effects as the birth control pill. It tends to make the periods very regular, lighter, and less crampy. There is a small decreased risk of uterine and ovarian cancer that is balanced by a slight increased risk of breast cancer. There is a very small risk of blood clots (DVT), and a tiny increased risk of heart attack and stroke. Overall these agents are extremely safe.