Question: I'm in 10th grade. How much will a W (Withdrawal) on a transcript hurt chances of getting into a college?
A "W" won't necessarily hurt you at all, but the key factor will be what's left on your schedule once you pull out of a class. For instance, let's say you're a biology buff and thus you decide to take both AP Bio and Environmental Science at the same time. But then you realize that you've bitten off more than you could chew. Dropping the Environmental Science won't hurt you. Dropping the AP Bio will be somewhat more significant since it's a "weighted" course which might affect your cumulative GPA and class rank. Even if your high school doesn't rank its students, your overall course load will be less demanding without this AP. The more selective colleges will probably notice this. Other colleges might not. And if you drop the only class you were taking in a major field (science, math, foreign language, etc.) then this will leave a visible void on your transcript. Dropping an elective such as psychology, yearbook, band, etc. wouldn't. In fact, if your schedule is full of rigorous major subjects, dropping an elective shouldn't have any effect on college outcomes.
Since you are still a sophomore, a Withdrawal of any sort will usually have less impact on college verdicts than it might in your junior or senior years. Admission folks especially don't like to see W's after a student has been admitted. I've known of seniors who got good news from top-choice colleges in the Early Decision or Early Action round and then decided to coast through the rest of the school year by dumping one or more of their more challenging classes. But Early acceptances are predicated on the student taking the same list of classes that appeared on the initial application. So a "W" after an early acceptance can be short for "Woe is me!" :(
But do keep in mind that, if you're stressed about your current course load but worried that dropping a class might torpedo college admission odds later on, you need to put your mental and physical health ahead of potential admission decisions.