You want to take the SAT I very soon. Some schools (especially a few on the west coast) do not accept the SAT and instead request that you submit an ACT score. The large majority of schools will take an SAT I score though. You will probably need to take up to three SAT II subject tests. You should consider what schools you might be interested in applying to and figure out what their requirements are, but do plan on taking the SAT I very soon. You will want to apply this fall/winter to college so you will need to get those SATs done soon. Don't forget to talk to your school's guidance counselor or even to teachers or an administrator to get advice. They help hundreds of your fellow students with these things!
you don tnecessarily have to take the SAT, find out which schools you're interested in first, most schools in the midwest take ACT and now a lot (most) other schools around the US are accepting it now too. I am applying this year to schools from NY to LA and all take the ACT. (however i am required SAT IIs) check the school first, then decide what test