Hello! This may be a very dumb question, but it’s been confusing me. When do you apply for college? I’m a sophomore, and I’m being told junior or senior year. But for example, one of the deadlines for admission for one of the colleges I’m considering is January 1st, do I apply before January 1st of my junior or senior year? Thank you! 
You apply Senior year, after you have completed your Junior year. If possible, try to have all your SAT/ACT testing done prior to Senior year to help target schools based on your GPA and test scores. Some schools application will open in August prior to Senior year, so you can start filling out the applications and writing your essays. Many applications will due be due as Early as Nov 1 or as late as February 1. Depends on the college.
Common App opens for you to start applying to colleges on August 1 of your senior year. However, I think they recently changed it so you can start filling out your profile as early as your junior year. You’ll have to check out the common app website to see exactly what the new system is, but don’t feel any pressure to start filling out any sort of application until fall of your senior year. For now concentrate on keeping your GPA up, doing well with your SAT/ACT, building up your ECs, and developing good relationships with people you will want to ask for rec letters in a couple of years.