Before you can apply to college, you need to understand how you are applying: by early decision, early action, regular decision, or rolling admission. Not only will your choice determine when your application materials are due, but it will also determine when you will find out if you are accepted.
A binding application option. If you apply and are accepted to a school through early decision, you must attend. Applications are usually due in November or December; application decisions come soon thereafter. This is a risky option if you need financial aid, as you are essentially accepting the decision before receiving a financial aid package. If you are accepted via early decision, most schools will have you withdraw your applications from all other schools.
Early action means you submit your application materials earlier in the year, and likely receive an admissions decision earlier as well. This is a non-binding application option. If you are accepted via early action you are still free to apply to other schools and compare financial aid packages before making your final decision.
The standard application option. Most colleges will have regular decision deadlines in January or February. One notable exception is the University of California system, which requires students to apply and submit all regular decision application materials by November 15.
Applications are accepted and reviewed on a first-come, first-served basis. Most institutions will accept applications until their class is filled. Some will even accept applications until the week before classes begin.