Most four year colleges have a window of opportunity for applying for the next semester, or for the next year.
There is an opening date when applications can be sent, and a closing date (deadline) for applications to be received.
You need to research what these dates are for the colleges in which you are interested. For many traditional colleges, the window dates fall somewhere between October and February for admission the following year.
Also, for most traditional colleges, most admissions aren't awarded until after the deadline (late Spring). This varies, however, because some students take the opportunity to apply for Early Decision. If admitted by Early Decision, the the student is locked into that school, because once the decision is accepted (before any other schools announce admissions), the student cannot change their decision.