When you are coming for business for a few days or tourism else to visit the United States of America, you need to apply for the B1/B2 visa. For any citizens of a foreign country who want to visit USA need to first take a valid visa, and only then, can they come to the country. You must follow the proper steps to qualify for the B1 and the B2 visa.
When you are coming to consult with your business associates, attend any professional, business, educational, scientific else conferences, when you want to settle a real estate project and when you want to negotiate any contract.
Most people who want to travel, enjoy a holiday, visit friends or family, come for short term medical treatments, participate in social service events, come for musical, sports or contests work, short duration of studies like a summer course which is not a credit course for a degree like cooking or writing workshops must take this visa.
If you are coming for studies for more than 1 month, employment or to hunt for jobs, professional paid performances, crewmember arrival of aircrafts or ship, working in a foreign film, radio, journalists, media, press, etc. is not allowed to opt for the visitor visa.
For any non-immigrant visa, you need to fill up the form DS- 160 along with uploading your proper photograph which fulfils the requirements for the application. You need to make sure you check with the immigration office as to what type of photo is needed for the B1 and B2 visa. Once you have the form approval, make sure you take a print out of it to keep it with you as you may require a proof later.
Note all these regulations to qualify for the visa and keep in mind that B1/B2 visa will allow you to stay in the country for a little span of time. Get all your information gathered properly before applying.