What is the procedure for sending armed forces for international military operations in USA?

I am interested how is the decision made in USA regarding sending military contigent for taking part in different military operations and missions. By which body is such decision taken and what is the procedure, what are the cases when army can be deployed to different parts of the world. I need the law, the text or just link or advise where to find such. Thanks in advanceWhat is the procedure for sending armed forces for international military operations in USA?there is no procedure.