There is no formal set of requirements for what to do after you have interviewed for a job. However, the basic idea is that you need to follow up the interview by contacting the interviewer at least twice for fairly specific purposes.
Most people who give advice on this issue say that it is important to follow up with an email message on the same day as your interview. This message should be a simple thank-you for the person’s time and for the opportunity to interview with them.
Second, you should send another email somewhat later on. This one should be more detailed. The purpose of this message is to act as something of a sequel to the cover letter that you wrote with your application. With the application, you talked about why you would be good for the job in question. In this message, you should review why you would be good for the job, but you should ideally be able to refer to things that happened at the interview itself. You might, for example, talk about some way in which you are particularly qualified to fill a need that they mentioned at the interview. You might add thoughts that you had about things that were discussed in the interview. Sometimes you do not think of something at the interview that would have been good to mention. This message is the place to add these things.
There are different schools of thought as to whether to call or whether to write “snail mail” letters. However, there is a clear consensus around the idea that there should be at least two follow up contacts that express your continuing interest in the job and which reinforce the idea that you would be good at the job.