Easy enough question.
As a fourth year student(beginning) you contact your school and get a packet to register for the match. Even before then, you can contact the programs you are interested in individually and ask for an application packet which should include an application and some information about the internship. After you send in your application, you go to the interviews you have been offered. Now, here is where it gets tricky.....sometimes you get offered the internship during the interview(usually if you have been at this institution or have a good letter from one of the docs) or the offer may come after the interview, or not at all. Unlike the MD match, the DO match is easier because you know sooner. Then, you either hand shake agreeing to come there or you sign the contract before the match. Then during the match, you send in the information putting that progam first.
Now, internships differ! Internships can be included in the residency or not. It means the difference between two applications(one for internship and one for residency) or one. There are traditional rotating, IM specific, ER specific, peds specific, OB specific, FP specific. It all depends one what you want to do. Hopefully this answers your question. If you have any others, you should check out the AOA webpage.
