Usually you do that in your 12 grade year CONSIDERING you've taken all of your ACT and SAT tests (or at least close to getting the grade you want). You can start looking around anytime, though, but for now I would just focus on your grades and study well- only look for colleges when you have the time- especially next year. Your junior year is the hardest.
Each college / university has their own deadline but they're usually not until grade 11 or 12. Take a look at the website of the college of your choice - most colleges usually have an admissions section. :D