First of all, I have an impresson that you are not enrolled in a US med school so I'm gonna give you some inforamtion accordingly.
It's basically a rotation that your school allows you to do anywhere you like. The number of elective rotations vary according to the med scool. You can do them at you school or elsewhere in the world. It makes you a more competitive applicant if you do your electives in the states oncw you apply for residency.
So to apply for residency you need to have your MD, your USMLE Step 1, 2 CK & CS, recommendation letters, and electives? Anything else?
Theoretically, Step 1 and letters of recommendations would be enough. However, you would be more competitive if you are ECFMG-certified(ie graduate and passed Step 1,2 and CS). Needless to say, US electives make you a better applicant as well. Other things to help polish your CV include research projects, publications and volunteer work.
How do you find a suitable one for you? How do you apply?Can you choose to do it in any department? How many electives do you need to do? Thanks again.
These details have been discussed thoroughly in some threads in the international forum. Anyway, you have to approach each med school separately. Each med school has their own requirements. the requirements may include any combination of the following: Application fee, tuition fee, TOEFL, Step 1, Malpractice insurance and health insurance.
Theoretically, you can choose any department you want. However, the rotation you are interested in might turn out to be full once you apply and have your application processed. I wouldn't worry much about this issue anyway.
Usually, each elective lasts 4 weeks. The more you do the better.