How do you hire a non US citizen?

Answer 1

You hire a non-citizen the same way you hire a citizen - offer them a job.

Your new employee will need to provide proof of eligibility to work in the US, however. Generally speaking, this will be a valid US Visa that specifically states the owner may hold a job, a U.S. Permanent Resident visa (which implicitly allows for job-holding), or evidence of US citizenship. See the CIS form I-9 for a complete list of acceptable means of proving eligibility to work.

If the non-US citizen has a valid visa for employment, they are treated exactly like any citizen employee.

If you wish to hire a non-citzen who does NOT currently have a valid work visa, you (the employer) may try to sponsor them for such a visa. This can be very difficult and expensive, and one should talk to an Immigration lawyer about the process for obtaining a valid work visa for a foreign alien worker.