Yes, by all means. Your freshman grades contribute to your overall high school grade point average. So if you decide not to get serious about your grades until your sophomore year (or even later), all those Bs, Cs, and Ds you earned before you got your act together will drag your GPA down.
Also, when evaluating your college application, the folks in the college admissions office will look at your entire transcript, not just your junior and senior year. And even though you may get straight As your senior year, those earlier lower grades will have an impact on the overall impression you give the admissions office.
Getting good grades in your freshman year (by studying hard, doing all your homework, and so on) will make it all the more easier for you to get good grades later in high school, as well as in college. That's because you'll be using the knowledge you gain early on in those later — and much harder — classes. So, in many ways, you'll be doing yourself a big favor by working hard even in your freshman year, when it may not seem all that important because college is still so far away.