The M-1 visa is available to people coming to the U.S. for vocational study. (This visa is authorized the the U.S. Immigration and Nationality Act; see I.N.A § 101(a)(15)(M), 8 C.F.R. § 214(m).) There is no limit on the number of people who can receive student visas in any one year.
You might not need to go through the whole process of applying for a student visa, however. If you come to the U.S. as a tourist, it's okay to take a class or two for recreational purposes. Similarly, people who have a spouse or parent in the U.S. with an A, E, G, H, J, L, or NATO visa or status, or workers in H status can attend school so long as they don't do anything that interferes with the other terms of their visa or nonimmigrant status.
Here are some of the pluses, minuses, and important considerations for holders of an M-1, vocational student visa:
To qualify for an M-1 vocational student visa, you first must have been accepted at a school that has received advance approval from the U.S. government. You must be coming to the U.S. as a bona fide student pursuing a full course of study. That means you must attend at least 18 hours per week, if the courses consist mostly of classroom study; or if the courses mostly laboratory work, 22 hours per week. Your intended school program must lead to a vocational objective, such as a diploma or certificate.
You must also already be accepted by the school of your choice and have enough money to study full-time without working. The U.S. consulate deciding on your visa will ask you to prove that you have enough cash on hand to cover all your expenses for up to a year.
You must be able to speak, read, and write English well enough to understand the course work (and, as a practical matter, the consular officer who interviews you for the visa, who will be informally testing your English ability). Alternatively, the school can offer special tutoring or instruction in your native language to help overcome any linguistic barriers.
In addition to proving you have the necessary background and financial capacity to pursue your studies, you must prove that you intend to return to your home country when your program is over. This is the same requirement for almost all nonimmigrant (temporary) visas (except a few that allow "dual intent"). If you are going to look for a way to take up permanent residence in the U.S. when your visa runs out, you are legally ineligible for an M-1 visa.
Again, you cannot start the visa application process until you have been admitted to a school that has received U.S.-government approval ("SEVP" or Student and Exchange Visitor Program certification) to accept foreign students. Once you have been accepted, and indicated that you will attend (usually by paying a deposit), the school will prepare a Form I-20 Certificate of Eligibility using its online Student and Exchange Visitor Information System (SEVIS) and send a copy of the form to you.
Take good care of this form, because you'll be submitting it as part of your visa application. Immigration officials will want to see the hard copy, despite the fact that they will verify the information using the online SEVIS system. The school should not charge you any money for issuing the I-20.
Here is what you will need to ready (in addition to your Form I-20) for your visa application and interview:
As the final step in obtaining an M-1 student visa, you will most likely need to attend a personal interview at a U.S. consulate. Expect to have the consular interviewer review the contents of your application and ask you about both your plans while in the U.S. and your intention to return home afterwards. The officer will also be double-checking that your English is good enough for U.S. study. If all goes well, you will be granted a student visa. You might also need to pay a visa issuance fee at this point.
For more information on this part of the process, see The Day of Your Consular Interview.
Your country's capital city probably has at least one U.S. embassy, and other major cities may have smaller consulates via the State Department's website at http://www.usembassy.gov/.
In some countries, you can to go straight to the consulate, present your application and paperwork, and receive a visa within a day. In others, the decision can take several weeks, or applications might need to be mailed in. Check with your local U.S. consulate via telephone or their website regarding its procedures.