This is the processing whereby, when you are a foreigner overseas, you interact with your home country U.S. Embassy or consulate to:
1. obtain travel visas to the U.S. for leisure and business,
2. obtain instructions about documents needed including medical reports, vaccinations, police reports, etc. based upon petitions filed on your behalf from citizens, permanent residents and employers in the U.S.,
3. pay visa processing fees and visa issuance fees when approved for a visa,
4. attend interviews and present documentation for review,
5. upon visa approval, receive your visa and a sealed visa packet for your presentation to the Customs and Border Protection Officer, upon inspection for U.S. entry.
Occasionally, other U.S. consulates can be utilized but often this delays processing and is not permitted. Some consulates in countries like China and India or Mexico charge an admission fee just to speak with the consulate personnel. Check with your home country consulate to verify if this is your situation. Often, the monies owed to the consulate are paid to a local bank before entry.