You get an offer letter that spells some of that out, but it isn’t a binding contract.
An employment relationship in the United States is presumed to be “at-will,” i.e., terminable by either party, with or without cause or notice. Indeed, a majority of employees in the United States are employed on an “at-will” basis, without a written employment contract, and only with a written offer of employment that outlines the basic terms and conditions of their employment.